why is it so hard to keep nutrients these days

[05XRunner]

So, I setup my Fluval 13 about 4 months ago. I just run floss and carbon once in a while and no skimmer. I fed twice a day pretty well and I finally got some test kits last week and zero on both and had to start dosing nitrate and phosphate. A few days ago I did end up adding one of those tiny airstone skimmers mainly for the oxygenation it provides but it seems to skim pretty good. Its crazy years ago we use to fight to keep nutrients under control now a days I cant seem to get them to stay, Is dry rock a culprit? since we all use to start with live rock back in the day

[jservedio]

32 minutes ago, 05XRunner said:

So, I setup my Fluval 13 about 4 months ago. I just run floss and carbon once in a while and no skimmer. I fed twice a day pretty well and I finally got some test kits last week and zero on both and had to start dosing nitrate and phosphate. A few days ago I did end up adding one of those tiny airstone skimmers mainly for the oxygenation it provides but it seems to skim pretty good. Its crazy years ago we use to fight to keep nutrients under control now a days I cant seem to get them to stay, Is dry rock a culprit? since we all use to start with live rock back in the day

Nah, it's not the rock. It's essentially just an increase in knowledge and better understanding the importance of nutrients for your corals and the overall health of your system. We now understand that proper nutrient balance and supply leads to an ecological succession as different populations of organisms boom, bust, and over time establish stable populations.

 

This is pretty simplified, but back in the day, few tanks had proper nutrient balance. Back even just 5-6 years ago, it was extremely common for people to run essentially 0 phosphates using GFO, AOH, Lanthanum Chloride, etc.  leading to an imbalanced and phosphorus limited tank. Without phosphates, the lowest level organisms that utilize the majority of nutrients in your tank are decimated allowing carbon and nitrates to build up while at the same time starving our corals. Essentially, we were freezing tanks in the earliest stages of ecological progression and hampering their maturity.

 

Now we understand that by letting nature take it's course, our tanks will be able to naturally process huge amount of nutrients which allow for healthier corals and other inverts.

 

This is why you now see tanks with no filtration at all that struggle to keep nutrient levels up and have to feed a ton just to keep some in the system when back in the day even the most sparse systems had trouble with nutrients and nuisance algae and it mostly boiled down to overfiltration.

[MrP]

Dry rock will absorb inorganic phosphate until it reaches a degree of saturation. 

[jservedio]

1 hour ago, MrP said:

Dry rock will absorb inorganic phosphate until it reaches a degree of saturation. 

While it's definitely true that aragonite soaks up inorganic phosphate, this wouldn't have any bearing on mature tanks and we see the exact same issues in tanks started with live rock. Plus, IME, dry rock reaches saturation (or at least slows down a ton) within 6-12 months depending on the bioload and how much sand you have, since that absorbs just as much phosphate.

 

Nutrient fluctuations are always an issue in the first year of a tanks life, generally in both directions, regardless if you start with dry or live rock. However, over the last few years, I've been noticing a huge number of people with tanks that are in the just-starting-to-mature 16-36 month range having lots of issues keeping their nutrients up that they didn't have early on. This is pretty much the polar opposite of the common excess nutrient issues people had with the same age-range tanks just 5-6 years ago (also started with dry rock).

 

The biggest non-equipment shift in reefing between now and 10-15 years ago is the way we think about nutrients. Plus, dry rock has been super common for more than a decade and DSB were popular before that, which meant far more clean aragonite to absorb phosphate compared to any modern tank with dry rock. I really don't think dry rock is a major factor in the long-term ability to keep nutrients up.

[Nano sapiens]

3 hours ago, 05XRunner said:

So, I setup my Fluval 13 about 4 months ago. I just run floss and carbon once in a while and no skimmer. I fed twice a day pretty well and I finally got some test kits last week and zero on both and had to start dosing nitrate and phosphate. A few days ago I did end up adding one of those tiny airstone skimmers mainly for the oxygenation it provides but it seems to skim pretty good. Its crazy years ago we use to fight to keep nutrients under control now a days I cant seem to get them to stay, Is dry rock a culprit? since we all use to start with live rock back in the day

 

jservedio hit on some points that highlight some of the differences from 'then' and now.  In addition, especially with nano/pico aquaria, past advice to 'not touch the sand bed' has thankfully been replaced by the knowledge that uneaten food/detritus needs to be periodically removed from the system and water changes are not just 'optional' for a small system's long term health.  Perhaps the most interesting question is 'What is the actual percentage of people with high PO4 and NO3 vs. those with low?'.  And how many people actually know/care?  Being active on Reef2Reef, I see plenty of large systems where lots of folks are still battling high PO4 and NO3 (especially nitrate since the fix is not always readily apparent).

 

Your system is still quite young at 4 months so hasn't established that 'mature equilibrium' yet.  Careful dosing/testing is fine, but as the system matures you may find that you can reduce/eliminate the dosing.

 

FWIW - I can count on one hand the number of times I've seen a PO4 reading with my 12g, 12+ year old system (no chem or mech filtration).  Same situation with nitrate in that for most of the system's lifetime it had very low to no reading at all (all Salifert kits).  In spite of this, corals were colored up well, healthy and growing.  And it's a non-issue for me as long as the corals are vibrant and healthy (the total phosphate and nitrate sources are often 'hidden' from our prying eyes, which is another story if you are interested).  Now if I go and mess with the system's equilibrium, then I can possibly cause an issue where phosphate and nitrogen are truly limited and the corals will definitely show it. 

 

 

 

 

 

 

[seabass]

25 minutes ago, Nano sapiens said:

the total phosphate and nitrate sources are often 'hidden' from our prying eyes, which is another story if you are interested

I'd like to hear your thoughts.

[05XRunner]

I vac my entire sandbed every waterchange. I guess i am guilty of probably taking to much out. I was doing 5g water changes on a 12g tank every 2weeks. 

I think I am just use to doing that much because my last tanks were a 40B then my Reefer 350 I had last year so 5g was always the min amount I would change 

[Nano sapiens]

1 hour ago, seabass said:

I'd like to hear your thoughts.

All this may be refined in the future, but for now this is how I see it:

 

Phosphate:  The big puzzler for many is why does one system with '0' PO4 have issues, while another with '0' PO4 does not?  In the later case, the phosphate must be available otherwise the coral would show the negative effects, so how does this work?.  The standard answer in the past has been 'because our test kits only show inorganic phosphate, aka orthophosphate, not organic phosphates'.  While this is undoubtedly true in many systems, when I had my system ICP-OES tested there was still only about 1/2 of the inorganic and organic phosphate one would expect as a minimum for a healthy fully stocked mixed reef.  So, I had to did a lot deeper on this and a vid on YouTube about carbon dosing/bacteria along with an Aquabiomics test rang the bell for me;  The extra needed phosphate is being provided by the coral ingested bacteria.  My system happens to have a ~75% Pelagibacteria population in the water column and they are both directly consumed and, when lysed by phages, their 'guts' are available for assimilation in the water column (which undoubtedly accounts for at least some of the phosphate measurable by ICP-OES).  With the continuous bacteria feeding by a relatively large coral/invert community, phosphate levels never have a chance to build up.  I have tried to get a test kit reading, but it requires that I add 3-4 times as much food as I normally do...and then soon after starts the hair and bubble algae...

 

Nitrate:  The statement I see often is; "I feed a lot, so how can all that nitrate be consumed and I see '0' on the test kit".  What is not always realized is that much of the nitrogen (predominately from food) is released as ammonia in our systems (mostly by the fish).  The ammonia is then directly assimilated by corals and other inverts (much easier to use than metabolically expensive nitrate), so there is less ammonia available for the bacteria in the nitrogen cycle to process...and so less nitrate than would be 'normally expected'.  When fed the same amount of food, a system that is relatively new and has just a few corals would be expected to have more of the nitrogen from food processed by bacteria and broken down into nitrate (nitrification), then eventually to di-nitrogen gas (often denitrification is inadequate and a build up of nitrate is the result).  A mature system with lots of corals/inverts that have assimilated much of the available ammonia will then typically have much less nitrate floating around in the water column, often very low to undetectable test kit readings.

[jservedio]

3 hours ago, Nano sapiens said:

Being active on Reef2Reef, I see plenty of large systems where lots of folks are still battling high PO4 and NO3 (especially nitrate since the fix is not always readily apparent).

I think a lot of this has to do with the fact that the "accepted" biomass of fish doesn't scale linearly with with volume and nobody with a big tank wants to admit that. In terms of fish biomass, two 3" long clownfish in a 20g tank is roughly the same as just two 9" tangs in a 540 gallon system and I've never seen a tank that big with just two fish! Even though the tangs are only 3x the size of the clownfish, their mass is actually roughly 27x (square-cube law).

 

In our nano systems, our fish biomass to volume ratio is on the extreme low end and our coral biomass to volume ratio is on the extreme high end. This allows our mature systems to basically be in a deficiency for nutrients (whether they are in bacteria, complex organic molecules, or inorganic molecules) and able to take anything we throw in there. Whereas a middle-larger sized tank is going to have a closer balance and a much larger tank to have an excess of nutrients.

 

I really appreciate your two detailed replies. Every time you post, I learn something new. Incredibly interesting information about bacterial uptake by your coral when there are a lack of organic phosphates. I had always assumed it was just our critters (including bacteria) taking up the organic molecules directly and never really having inorganics that are testable as the system matured. Never thought about the corals consuming bacteria directly - I had always assumed anything under 100 or so microns or so was out of reach for corals.

 

 @seabass, you too - I'd love to hear your opinions on this!

[seabass]

Thanks for that Nano sapiens and jservedio.

 

Lately, I've seen phosphate recommendations anywhere from 0.05 to 0.10 ppm (while I've been recommending a minimum of 0.03 ppm phosphate).  I get that we're starting to recognize the importance of nutrients, and that these levels ensure their constant availability.  Previously, I thought availability was more important than the level; however, this study shows faster growth rates at higher phosphate levels.

 

 

We've known that algae growth is affected by phosphate levels; but now it seems that we are realizing that coral growth is also impacted by inorganic nutrient levels.  And since coral health is often associated with growth, we might conclude that health is improved when phosphate levels are elevated.

 

I figure that some tanks which test 0.00 ppm for phosphate (like Nano sapiens' 12g) still might have a decent amount of phosphate input, so phosphate isn't necessarily always unavailable.  But as you stated,

1 hour ago, jservedio said:

Never thought about the corals consuming bacteria directly

I think a lot of us (including myself) tend to ignore the contribution of consumed organic phosphate from: coral food, phytoplankton, zooplankton, and bacteria.

 

I agree with you that intentionally starving tanks of nutrients in an attempt to limit algae has traditionally caused problems (poor coral health and even pests), broken food chains, and has hampered tank maturity.

 

[Jakesaw]

7 hours ago, MrP said:

Dry rock will absorb inorganic phosphate until it reaches a degree of saturation. 

Interesting. 

 

So as somebody who started with dry rock and has a young tank, this may be the reason I have never measured a speck of Phosphate in my aquarium.  So are you saying in 6 - 12 months or whenever marcorock is saturated, I should start to see phosphate start to show up in my tank,

 

I had stopped testing for it b/c wasn't getting a reading.  Maybe I should start back up to see when it shows up in my aquarium.

[Nano sapiens]

 

3 hours ago, jservedio said:

I think a lot of this has to do with the fact that the "accepted" biomass of fish doesn't scale linearly with with volume and nobody with a big tank wants to admit that. In terms of fish biomass, two 3" long clownfish in a 20g tank is roughly the same as just two 9" tangs in a 540 gallon system and I've never seen a tank that big with just two fish! Even though the tangs are only 3x the size of the clownfish, their mass is actually roughly 27x (square-cube law).

 

In our nano systems, our fish biomass to volume ratio is on the extreme low end and our coral biomass to volume ratio is on the extreme high end. This allows our mature systems to basically be in a deficiency for nutrients (whether they are in bacteria, complex organic molecules, or inorganic molecules) and able to take anything we throw in there. Whereas a middle-larger sized tank is going to have a closer balance and a much larger tank to have an excess of nutrients.

 

I really appreciate your two detailed replies. Every time you post, I learn something new. Incredibly interesting information about bacterial uptake by your coral when there are a lack of organic phosphates. I had always assumed it was just our critters (including bacteria) taking up the organic molecules directly and never really having inorganics that are testable as the system matured. Never thought about the corals consuming bacteria directly - I had always assumed anything under 100 or so microns or so was out of reach for corals.

 

 @seabass, you too - I'd love to hear your opinions on this!

 

Agreed that many large systems are WAY overstocked with fish.  Understandable though, as people generally keep large tanks so that they can keep many of the spectacular larger reef fish that they couldn't in a nano.  So they are constantly locked in a war on nutrient excess and this has fueled the plethora of nutrient control methodologies/products.  I have seen my share of fish overstocked nano's, too, but the higher coral/water volume ratio (compared to large systems), along with typically larger and more frequent water changes, tends to at least slow the rise of excess phosphate and other nutrients.

 

Glad you found my ramblings of interest.  Once I lock onto a conundrum that I know must have an answer, I'll doggedly pursue it for years if need be.  

 

Interestingly, bacterioplankton make up around 20% (or more) of a coral's total nutrient uptake.  Never ceases to amaze me that these animals can use so many different feeding techniques to get the nutrients that they require.

[seabass]

13 minutes ago, Jakesaw said:

 

So as somebody who started with dry rock and has a young tank, this may be the reason I have never measured a speck of Phosphate in my aquarium. 

It could also be your test kit.  Phosphate is relatively hard to test for, and some kits can't detect low values.  For example, API's kit goes up in 0.25ppm intervals; while Salifert is better, as you can start seeing a color change at 0.03ppm.  However, we really started seeing better low range results from Hanna's ULR Checkers.

 

And while calcium carbonate does bind phosphate, I purchased some dry rock (more than 15 years ago) which actually leached phosphate from the start.  That made a good surface for algae to grow on.  However, other phosphate-free dry rock acts more like MrP described.

[Nano sapiens]

3 hours ago, seabass said:

Thanks for that Nano sapiens and jservedio.

 

Lately, I've seen phosphate recommendations anywhere from 0.05 to 0.10 ppm (while I've been recommending a minimum of 0.03 ppm phosphate).  I get that we're starting to recognize the importance of nutrients, and that these levels ensure their constant availability.  Previously, I thought availability was more important than the level; however, this study shows faster growth rates at higher phosphate levels.

 

 

We've known that algae growth is affected by phosphate levels; but now it seems that we are realizing that coral growth is also impacted by inorganic nutrient levels.  And since coral health is often associated with growth, we might conclude that health is improved when phosphate levels are elevated.

 

I figure that some tanks which test 0.00 ppm for phosphate (like Nano sapiens' 12g) still might have a decent amount of phosphate input, so phosphate isn't necessarily always unavailable.  But as you stated,

I think a lot of us (including myself) tend to ignore the contribution of consumed inorganic phosphate from: coral food, phytoplankton, zooplankton, and bacteria.

 

I agree with you that intentionally starving tanks of nutrients in an attempt to limit algae has traditionally caused problems, broken food chains, and has hampered tank maturity.

 

 

I would agree with you that for most reefers, especially those with newer systems, having some measurable NO3 and PO4 is the best policy.  I think that having a plausible explanation as to why some very mature systems can do very well at very low/undetectable levels is most helpful as it takes the mystery out of what only looks like a potentially disastrous situation.  Unfortunately, clarity has not been a strong point in reef keeping, so anything we can do to 'clarify the unclarity' is most welcome, IMO.

 

While I agree that sustained growth can be used as a proxy for health, what I found is that it isn't a prerequisite. I remember reading an excerpt in one of the Reef Aquarium series books where they mention that similar Acropora corals on various natural reefs in divergent locations can have widely different growth rates (varying from 1/8"/yr to 7-8"/yr), yet you couldn't tell by looking at the corals if one was healthier than the other.  When I realized way back then that the race for the fastest growth was a bit of a red herring, reefing became less stressful and a lot more enjoyable 🙂

 

And I surely hope that no one thinks that the outdated and erroneous idea of starving a reef aquarium is a good thing.  Starting with a good foundation of bacteria found on a natural reef, sufficient/varied/regular food input, adequate waste export and a varied compliment of herbivores is the way to go, IME.

[Nano sapiens]

1 hour ago, Jakesaw said:

Interesting. 

 

So as somebody who started with dry rock and has a young tank, this may be the reason I have never measured a speck of Phosphate in my aquarium.  So are you saying in 6 - 12 months or whenever marcorock is saturated, I should start to see phosphate start to show up in my tank,

 

I had stopped testing for it b/c wasn't getting a reading.  Maybe I should start back up to see when it shows up in my aquarium.

Once your substrates (rock, sand) are phosphate saturated, the system will have reached an equilibrium level (whatever that might be) with the phosphate that is in the water column.  Add some phosphate rich food, for example, and the water column PO4 will temporarily rise until the bacteria, coral and other organisms consume/sequester it and equilibrium is restored.  Add some phosphate removal media, and phosphate bound to your substrates will liberate into the water column to try and maintain equilibrium (add a whole lot of this media and you can sequester so much phosphate that the system becomes phosphate deficient...seriously no bueno!).  On the flip side, add a whole lot of phosphate on a regular basis that the system can only partially process...wala, the cause of the classic overabundance of phosphate (to track this, we can only measure inorganic phosphate, aka PO4, with our test kits, but it's good enough for our purposes).

[seabass]

Thanks again everyone.  I know I got a little off topic, but I really appreciate this discussion.  It seems that recently my understanding about the importance of nutrients has been changing; and I find threads like this to be very helpful.

 

However, I still struggle a bit with the balance of feeding and dosing nutrients.  Obviously feeding is essential, but over feeding can directly add to excessive organic waste.  I'm starting to feel that modest dosing of nutrients to supplement feeding (while maybe not trying to target a specific value) might be helpful in tanks that return undetectable inorganic nutrient levels.

 

Although I still haven't bought into dosing phosphate beyond 0.03 ppm (except maybe when treating dinos).  I also realize that a higher level isn't necessarily a problem which has to be solved.  I remember when people were trying to explain how seemingly healthy, mature systems could exist with phosphate levels as high as 0.10 ppm (when the recommendation at the time was to limit phosphate below 0.03 ppm).

 

IDK, maybe phosphate levels are a little like pH levels in how we used to try to manage them; and maybe now we are looking less at achieving specific values and focusing more at providing enough availability.  I'm not even sure what an ideal level might be.  Typically we try to mimic natural reef parameters; however, our tanks don't tend to have the availability (nor diversity) of food that our wild reefs enjoy.

[Nano sapiens]

3 hours ago, seabass said:

Thanks again everyone.  I know I got a little off topic, but I really appreciate this discussion.  It seems that recently my understanding about the importance of nutrients has been changing; and I find threads like this to be very helpful.

 

However, I still struggle a bit with the balance of feeding and dosing nutrients.  Obviously feeding is essential, but over feeding can directly add to excessive organic waste.  I'm starting to feel that modest dosing of nutrients to supplement feeding (while maybe not trying to target a specific value) might be helpful in tanks that return undetectable inorganic nutrient levels.

 

Although I still haven't bought into dosing phosphate beyond 0.03 ppm (except maybe when treating dinos).  I also realize that a higher level isn't necessarily a problem which has to be solved.  I remember when people were trying to explain how seemingly healthy, mature systems could exist with phosphate levels as high as 0.10 ppm (when the recommendation at the time was to limit phosphate below 0.03 ppm).

 

IDK, maybe phosphate levels are a little like pH levels in how we used to try to manage them; and maybe now we are looking less at achieving specific values and focusing more at providing enough availability.  I'm not even sure what an ideal level might be.  Typically we try to mimic natural reef parameters; however, our tanks don't tend to have the availability (nor diversity) of food that our wild reefs enjoy.

 

From what I've seen, it really is a case by case basis regarding phosphate levels for mature systems.  You are correct that the 'best' phosphate level for these systems is not something that is set in stone, but is best determined by how well the corals do over time as well as general system health.

 

I think that making the distinction between a newer system with undetectable PO4 and a mature one with undetectable PO4 is very important.  In the first case, having at least detectable levels has been shown to be beneficial, but in the second it isn't a requirement if the corals are healthy/colorful and have growth...and the system is run in a stable manner.

 

My personal inclination is to allow a system to find it's own natural phosphate level without having to supplement with a commercial product.  Observing the corals for signs of phosphate deficiency is key and adding more fish and/or change to more phosphate rich foods in an attempt to improve the situation can resolve the issue.  However, I think supplementation by use of a phosphate product may be appropriate in those cases where adding fish/more food causes runaway nitrate issues that the aquarist can't resolve or where additional foods encourage pests to proliferate (looking at you, hydroids!) 🙂

 

Mimicking low nutrient natural reef water nutrient levels can be quite successful, but with the caveat that phosphate, nitrogen and other nutrients need to be available by some means.  Can be that a system naturally has sufficient levels of water column bacteria to meet the corals' nutritional needs or the nutrients are provided via regular dosing.  But for the typical reef keeper, simply maintaining detectable, but not excessive PO4 and NO3 is much easier and less worrisome, IMO.

[SaltyGallon]

Thanks for the contributions to this thread guys, it has been a really interesting read.

[Thrassian Atoll]

Yup, I have to dose daily to keep my nutrients where I want them.  

[jservedio]

17 hours ago, Nano sapiens said:

My system happens to have a ~75% Pelagibacteria population in the water column and they are both directly consumed and, when lysed by phages, their 'guts' are available for assimilation in the water column (which undoubtedly accounts for at least some of the phosphate measurable by ICP-OES).  With the continuous bacteria feeding by a relatively large coral/invert community, phosphate levels never have a chance to build up.

 

12 hours ago, Nano sapiens said:

Interestingly, bacterioplankton make up around 20% (or more) of a coral's total nutrient uptake.  Never ceases to amaze me that these animals can use so many different feeding techniques to get the nutrients that they require.

 

I was thinking about this some more last night - did you happen to save any of the research you had done or found on this? Like I had mentioned, I had always assumed that anything between very large organic molecules still measured in angstroms utilized directly by zooxanthella and 100-150ish microns caught by the smallest polyps was pretty much out of reach for corals. But, it makes perfect sense that a a 10-12 micron dinoflagellate would have no problem consuming a 1/2 micron bacteria. It's incredible just how diverse a coral's energy source can be!

 

 

14 hours ago, seabass said:

however, this study shows faster growth rates at higher phosphate levels.

 

Appreciate the response. I've actually read this study and seen this graph - I think it was you who had shared it with me before! I also haven't seen many other studies like this in the past 10 years. I wouldn't be surprised if the extreme increase in skeletal growth had something to do with how easy it is to incorporate P into the skeletal structure of coral allowing for more growth using the same amount of energy. Coral skeleton (at least acropora and montipora) in high-phosphate tanks is significantly less dense and far, far more brittle so there are always drawbacks and not just in the sense that you can see a less dense structure under a microscope. The slightest bumps by small fish (or even just strong flow from a bucket being dumped during a WC) will snap acro branches like they are nothing. Since my 20g, I've actually stopped keeping my phosphates as high as they were, which were definitely kept artificially high by utilizing the massive pool of detritus in my sump. Had I cleaned it from time to time, I probably would have had similar inorganic phosphate and nitrate levels as nano_sapiens.

 

 

One other thing that I think factors into why modern nano tanks are able to rip through so many nutrients is because we are putting much more light energy into the system by using LEDs. 12-15 years ago, if you had an MH or 4-6 bulb T5 over your nano, you were on the top-end for lighting when most people were still using PC. Now that pretty much everyone is using LEDs, the average PAR in nanos has definitely increased quite a bit.

 

Overall, it's a super interesting topic, but I think we can all agree that this big change over the year mostly has to do with an increase in knowledge!

[seabass]

49 minutes ago, jservedio said:

Coral skeleton (at least acropora and montipora) in high-phosphate tanks is significantly less dense and far, far more brittle so there are always drawbacks and not just in the sense that you can see a less dense structure under a microscope. The slightest bumps by small fish (or even just strong flow from a bucket being dumped during a WC) will snap acro branches like they are nothing.

@jservedio, I'm not sure that we observe this dramatic effect when maintaining the more typical phosphate levels that we usually have in our systems.  I don't actually know anybody who is maintaining their tank's phosphate levels at 0.50 parts per million (or about 5 times higher than what's typically considered "high", or around 10 times higher than the upper end of what's frequently recommended).  However, I do appreciate you bringing up this point, which is also echoed in that study.  This phenomenon might contain similarities to weaker lumber being associated with high growth trees (as determined via their growth rings).

 

@mcarroll, I know that in the past, you have commented on calcification within higher phosphate environments.  I was looking for the post, but couldn't find it.  Care to comment on this topic?

 

 

[jservedio]

45 minutes ago, seabass said:

I'm not sure that we observe this dramatic effect when maintaining the more typical phosphate levels that we usually have in our systems. 

I can tell you that I definitely experienced this in my 20g and I can't even imagine what acro skeleton formed in 0.5ppm PO4 would be like! I don't notice any difference at all in growth (likely because my PO4 was never really far above 0.15pm for an extended period of time), but the density and brittleness of the skeleton is dramatically different even at 0.1ppm. Unlike most, my tank was at 0.1ppm for at least 5 years and I never started with more than a 3/4" frag, so my entire colonies are as brittle as glass. It's a huge pain in the ass when every week or two you are finding 3 or 4 acro or monti frags in the sand. The back left corner of my tank is sort of a dead spot for flow and things build up there (by design - out of sight!), and I've got an actual pile of frags and shards of coral skeleton. Just did a water change last week and I've already got 7 1/4"-1" frags sitting in a pile already.

 

I actually stopped running my tank with phosphates that high specifically for this reason! Most of my SPS never get long branches because they simply break as they get too long. This was worst in my FF Digi which has grown 2-3" long branches, then they just break off and fall over. It's done this 4 or 5 times over the last 3 years!

[seabass]

Thanks, I meant to ask you what level of phosphate you felt resulted in brittle skeletons.  That's good first hand (quantifiable) experience which definitely adds to the discussion.  And it's good to have an upper limit defined.  Although I suppose it's possible that there might be contributing factors.

 

Just curious, how was the coralline in this tank with phosphate which was maintained at 0.15 ppm?

[Nano sapiens]

4 hours ago, jservedio said:

I was thinking about this some more last night - did you happen to save any of the research you had done or found on this? Like I had mentioned, I had always assumed that anything between very large organic molecules still measured in angstroms utilized directly by zooxanthella and 100-150ish microns caught by the smallest polyps was pretty much out of reach for corals. But, it makes perfect sense that a a 10-12 micron dinoflagellate would have no problem consuming a 1/2 micron bacteria. It's incredible just how diverse a coral's energy source can be!

 

Good question.   In respect to corals, bacterioplankton is commonly thought of as being attached to particulate matter which can be snared by coral surface mucus/and or specialized 'mucus nets' and in this way ingested.  In the literature, this is often mentioned as an 'indirect' method of bacterioplankton consumption utilized by filter-feeders: 

 

https://reefs.com/magazine/the-carbon-continuum-heterotrophic-bacterioplankton-and-reef-food-webs/

 

 

However, I did find a reference that points tantalizingly towards the possibility of true direct bacterioplankton consumption:

 

https://www.sciencedirect.com/science/article/abs/pii/S0167701216301294

 

"Also, we observed that SYTO^®62 allowed distinguishing two main bacterial groups in < 10% of the generated cytograms (data not shown), which may correspond to the ubiquitous high and low nucleic acid content bacteria, commonly found in planktonic cells (Bouvier et al., 2007)."

 

I believe that more study is needed to determine conclusively that bacterioplankton (all by itself) is actually consumed in this way.  Another possibility I can think of is that the mucus captured bacterioplankton cells are lysed by the coral holobiont's viral and bacterial phage populations making at least some of their contents available to the host coral.  Other holobiont members, such as fungi and protists, may also play a role in captured bacterioplankton nutrient assimilation.

 

The main takeaway for me is that to survive and prosper in a watery world where available water column nutrients are so scarce, coral (I should say the 'coral holobiont') is supremely well adapted to take advantage of every possible nutritive source (and I doubt that we have discovered all of them, yet).  No wonder corals (in one form or another) have survived all the earth's major extinction events for the last 535 million years.

[jservedio]

1 hour ago, seabass said:

Thanks, I meant to ask you what level of phosphate you felt resulted in brittle skeletons.  That's good first hand (quantifiable) experience which definitely adds to the discussion.  And it's good to have an upper limit defined.  Although I suppose it's possible that there might be contributing factors.

 

Just curious, how was the coralline in this tank with phosphate which was maintained at 0.15 ppm?

Honestly, I don't really know where the cutoff would be or where it becomes noticeable, I just know that multi-year growth with  >=0.1ppm PO4 makes acros and montis in particular incredibly brittle. I'll try and pay more attention now that I'm bringing my phosphates down quite a bit in the 50g to see if it persists or if it was the phosphate that was solely responsible for the issue, but I'm not sure what else would lead to skeletal problems like that since my other parameters are within the typical ranges (albeit alk on the lower end). I will say that my growth speed for SPS is definitely below average because I keep my lighting comparatively very low to other SPS dominant tanks because I push for really good LPS coloration, but I don't think that would lead to brittleness issues since I never had brittleness until I brought my nutrients way up.

 

My coralline growth was actually very low for a tank it's age. My rocks were purple just from the sheer length of time they were in the tank, but never got coralline on my back glass and it was minimal on my overflow, return, and sand. This was a blessing in disguise though since combined with the slower growth I was never using more than ~1.5dkh/day so I was able to keep using Kalk alone even with a bunch of decently sized SPS colonies.

 

1 hour ago, Nano sapiens said:

However, I did find a reference that points tantalizingly towards the possibility of true direct bacterioplankton consumption:

 

https://www.sciencedirect.com/science/article/abs/pii/S0167701216301294

 

"Also, we observed that SYTO^®62 allowed distinguishing two main bacterial groups in < 10% of the generated cytograms (data not shown), which may correspond to the ubiquitous high and low nucleic acid content bacteria, commonly found in planktonic cells (Bouvier et al., 2007)."

 

I believe that more study is needed to determine conclusively that bacterioplankton (all by itself) is actually consumed in this way.  Another possibility I can think of is that the mucus captured bacterioplankton cells are lysed by the coral holobiont's viral and bacterial phage populations making at least some of their contents available to the host coral.  Other holobiont members, such as fungi and protists, may also play a role in captured bacterioplankton nutrient assimilation.

 

The main takeaway for me is that to survive and prosper in a watery world where available water column nutrients are so scarce, corals (I should say the 'coral holobiont') is supremely well adapted to take advantage of every possible nutritive source (and I highly doubt that we have discovered all of them, yet).  No wonder corals (in one form or another) have survived all the earth's major extinction events for the last 535 million years.

Wow, that is amazingly cool - thanks a lot for that link. It's so fascinating how little we actually know about what is going on with coral. While indirect bacterial consumption is straightforward and makes sense to any reefer, the idea of direct bacterial consumption is incredibly interesting, And even if it isn't happing, your hypothesis of obtaining nutrition from the lysing of bacterial cells is just crazy to think about. I'm glad you brought up "coral holobiont" and I think in the reefkeeping hobby, we should start thinking of corals less as just "an animal" and more as a whole ecosystem unto itself far beyond just the polyps and zooxanthellae. It seems pretty clear there is so much more going on than polyps simply eating meaty plankton and zooxanthellae photosynthesizing to make sugars.

 

The idea that a single coral is capable of producing it's own food through photosynthesis and also able to take nutrition from molecules just a few angstroms in size all the way up to macroscopic particles measured in inches and everything in between is pretty wild.