Alkalinity target and consumption rate

[Hoosier]

I've got a BioCube 29, started about 18 months ago, that has some soft corals, LPS (hammer coral, "candy cane" coral), a zoanthid plug, crabs, & snails.  The soft corals (Anthelia, Sinulina, green star polyp, mushrooms) are all growing well.  The hammers look healthy, but haven't notably grown in about a year.  The zoanthids plug has been in for ~ 8 months & has never done much of anything.  The candy canes are relatively new (~3 months, same as the Anthelia) and haven't notably changed.

 

I decided to test whether mineral limitation could be limiting the LPS/Zoa performance.  I'm using Red Sea Coral Pro salt, and decided to go all-in on Red Sea ... with dosing the Foundation ABC supplements, based on testing & monitoring levels with the Red Sea foundation pro multi-test kit.  

 

I'm struggling to hit the targets suggested by Red Sea for mixed reef parameters (Ca @ 450 ppm, dKH @ 11.5, Mg @ 1350 ppm), with alkalinity being the real challenge.  Following the Red Sea direction, I set out to hit the targets, then wait four days to measure consumption & determine daily dosing.  Each supplement has a maximum amount to add in one day to minimize shock to the ecosystem.  However, after more than two weeks of trying, I still haven't gotten up to the recommended level for dKH, because the consumption rate appears to be higher than the maximum you're supposed to dose in a day -- which seems strange, because I don't have a particularly densely packed reef.  After reading through a bunch of old threads, I have some questions:

 

1.  Is Red Sea's suggestion of an alkalinity of 11.5 actually reasonable for a mixed reef?  I found very little discussion of what targets should be, much discussion of test accuracy.

 

2.  What rates of alkalinity consumption are realistic?  I seem to be getting variable rates of consumption, but typically exceeding 1 point/day, and sometimes nearing 3points. This is crazy, because I know that when I mix the RSCP salt it starts at a dKH ≈ 10.5, and prior to starting on this dosing path the dKH in the aquarium would hover around 7-9 (based on SeraTest), so the system wasn't continuously consuming >1 point dKH/day before I started dosing.  E.g., yesterday dKH started at 8.7, I added 20mL Foundation B, predicting a rise of dKH of 2.0, and after dosing, I measured the alkalinity at 10.6; then today it was 7.7.  The increase following dosing matches the expectation based on the amount of Foundation B dosed, suggesting my testing is accurate, or at least consistently biased.)

 

3.  Would dosing increase the consumption rate?  That is, is there a non-linear relationship between availability and consumption?

 

I've attached a photo of the aquarium to give a sense of just how much stuff is in there.  Any thoughts or suggestions are appreciated.

 

--Hoosier

 

 

[paulsz]

44 minutes ago, Hoosier said:

1.  Is Red Sea's suggestion of an alkalinity of 11.5 actually reasonable for a mixed reef?  I found very little discussion of what targets should be, much discussion of test accuracy.

 

11.5dkh is fairly high. Not "unsafe" high, but fairly high. Typically people choose anywhere between 8-11 dkh. What's yours at the moment? And what's your calcium and magnesium at?

 

44 minutes ago, Hoosier said:

What rates of alkalinity consumption are realistic?  I seem to be getting variable rates of consumption, but typically exceeding 1 point/day, and sometimes nearing 3points. This is crazy, because I know that when I mix the RSCP salt it starts at a dKH ≈ 10.5, and prior to starting on this dosing path the dKH in the aquarium would hover around 7-9 (based on SeraTest), so the system wasn't continuously consuming >1 point dKH/day before I started dosing.  E.g., yesterday dKH started at 8.7, I added 20mL Foundation B, predicting a rise of dKH of 2.0, and after dosing, I measured the alkalinity at 10.6; then today it was 7.7.  The increase following dosing matches the expectation based on the amount of Foundation B dosed, suggesting my testing is accurate, or at least consistently biased.)

The only way you'll know what you're consuming is by testing. Test at the same time of day. If you want, test one morning and then a few days later (or the day after) test at the same time. Divide the difference by the amount of days between the two tests.

For your tank, 1 dkh a day seems high. From the jam packed SPS reefs I see here and on other sites, some people say they use 1-2 dkh a day. So for your tank with minimal corals, mostly softies with some LPS, it seems wrong that you're using anywhere between 1-3 dkh per day. 

What may be happening is precipitation. Do you dose calcium? How much and how long after you dose the alkalinity?

44 minutes ago, Hoosier said:

Would dosing increase the consumption rate?  That is, is there a non-linear relationship between availability and consumption?

Higher alkalinity and calcium have shown to increase growth rates. Is it so much that you'll notice a big consumption jump? I doubt it. But i can't tell for sure because i've never done it or experimented with it.

 

to summarize:

- what are you current parameters for alk/cal/mag?

- How often do you dose calcium? how much do you dose (in ppm)?

- When do you dose calcium? Same time as alkalinity? before, after? How much time between the two?

- Where do you do the dosing? in the main display? Do you have a powerhead in there? (can't see one in the pic but it may be cropped out)

 

[pokerdobe]

Nothing in your tank suggests that alkalinity should be used at the rates you're reading. More than likely, alk is simply precipitating out. 

 

5 hours ago, Hoosier said:

1.  Is Red Sea's suggestion of an alkalinity of 11.5 actually reasonable for a mixed reef?  I found very little discussion of what targets should be, much discussion of test accuracy.

It's achievable but most tanks run a middle ground. I find no reason to keep my alk that high and I run my alk in the low 7's lately. 

 

5 hours ago, Hoosier said:

2.  What rates of alkalinity consumption are realistic? 

Depends on how many stony corals you have and how happy they are. My tank currently consumes about 1.2-1.3 dKH point per day. 

 

5 hours ago, Hoosier said:

3.  Would dosing increase the consumption rate?  That is, is there a non-linear relationship between availability and consumption?

Not really. There's some correlation with higher alk and more growth, but your corals need to be in a healthy state to consume it. 

[kimberbee]

Test the alk of your freshly made saltwater. Many people find RSCP doesn't actually mix up as high as it claims to. 

[Clown79]

Your alk target should be what the salt mixes at. Therefore less fluctuations with waterchanges.

 

Stability is more important than reaching some magic number.

[Hoosier]

Thanks everyone for the perspectives & suggestions.  I will worry less about trying to hit 11.5 as a target.  I I think I'll try a couple of larger-than-usual water changes and then simply aim for an equilibrium based on multi-day measurements of consumption... perhaps I'm testing frequently enough that I'm running into measurement noise.

 

Some further information:  The salt is mixing up at dKH = 10.5, but I've only measured it with the precise Red Sea test at the most recent water change (2 & a half weeks ago now).  Before I started dosing, Calcium & Magnesium were at 425 and 1320 ppm respectively.  Dosing works to get them up to the Red Sea recommended levels for mixed reefs of 450 & 1350 respectively.  Consumption of those is much less dramatic (though still inconsistent day-to-day), and doesn't reflect the supposedly stable ratio of consumption among the three components.

 

Alkalinity precipitation could certainly cause what I'm seeing, but what would cause precipitation?  (The pH is stable at 8.2-8.3.)  Is there a way to avoid it? It obviously doesn't make sense to try dosing alkalinity if it's just going to precipitate out. 

 

--Hoosier

[paulsz]

How long do you wait between dosing alkalinity and calcium? 

[Hoosier]

22 hours ago, paulsz said:

to summarize:

- what are you current parameters for alk/cal/mag?

- How often do you dose calcium? how much do you dose (in ppm)?

- When do you dose calcium? Same time as alkalinity? before, after? How much time between the two?

- Where do you do the dosing? in the main display? Do you have a powerhead in there? (can't see one in the pic but it may be cropped out)

 

As of the tests I just did:  7.3 / 480 / 1380.  I don't have a regular schedule for dosing Ca since I was still trying to hit the suggested "start point" for measuring consumption.  In practice this has been daily or every couple of days, anywhere from 0 to 20ppm.  Per the Red Sea instructions, I've been dosing Mg, then Alk, then Ca, about 10-15 minutes apart.  Dosing is added to the sump compartment in the back of the BioCube.  There is also an extra powerhead behind the rock that can't be seen in that photo.

 

[Clown79]

46 minutes ago, Hoosier said:

Thanks everyone for the perspectives & suggestions.  I will worry less about trying to hit 11.5 as a target.  I I think I'll try a couple of larger-than-usual water changes and then simply aim for an equilibrium based on multi-day measurements of consumption... perhaps I'm testing frequently enough that I'm running into measurement noise.

 

Some further information:  The salt is mixing up at dKH = 10.5, but I've only measured it with the precise Red Sea test at the most recent water change (2 & a half weeks ago now).  Before I started dosing, Calcium & Magnesium were at 425 and 1320 ppm respectively.  Dosing works to get them up to the Red Sea recommended levels for mixed reefs of 450 & 1350 respectively.  Consumption of those is much less dramatic (though still inconsistent day-to-day), and doesn't reflect the supposedly stable ratio of consumption among the three components.

 

Alkalinity precipitation could certainly cause what I'm seeing, but what would cause precipitation?  (The pH is stable at 8.2-8.3.)  Is there a way to avoid it? It obviously doesn't make sense to try dosing alkalinity if it's just going to precipitate out. 

 

--Hoosier

Then your target is 10.5 to maintain that.

 

You really should only be dosing to replenish what your corals are using rather than trying to get to what red sea targets are, which are considered high.

 

There are ppl with beautiful tanks that keep there levels far lower than that.

 

Your ca and mag are fine too.

 

Doing large waterchanges to fix something that isn't broken, can lead to far more significant problems. 

 

I'd focus on stability, monitoring daily alk consumption.

 

 

[Clown79]

39 minutes ago, paulsz said:

How long do you wait between dosing alkalinity and calcium? 

Depending on product, where and how you dose,  you can do it 5 mins apart.

 

Esv dosed in tank in high flow can be done 5 mins apart. 

 

In sump dosing- should wait until the water is dispersed so an hr or more.

[paulsz]

24 minutes ago, Clown79 said:

Depending on product, where and how you dose,  you can do it 5 mins apart.

 

oh okay, good to know. I did not know that. Thanks!

[Hoosier]

32 minutes ago, Clown79 said:

 

I'd focus on stability, monitoring daily alk consumption.

 

So my water change schedule has been 20% every 4 weeks (+/- 3 days).  If new water mixes up at a dKH = 10.5, and do a 20% change to a tank that is at dKH = 7.5, it should work out to an alkalinity of 8.1 after the water change.  Then I aim to hold that stable, until the next water change, at which point a 20% change should raise the dKH up to ~8.6, then aim to hold that stable, and so on, until I'm holding stable at the 10.5 the saltwater originially mixes up to.  Does that sound reasonable?

 

--Hoosier

[paulsz]

15 minutes ago, Hoosier said:

Does that sound reasonable?

you could also dose a bit to get it up to 10.5 over a few days, instead of waiting on water changes. 

 

note that you should also aim to have your cal and mag at the same level as your salt mix. Next time you make saltwater, test all three and write those down somewhere. That way you'll know to always aim for those. 

 

[Clown79]

50 minutes ago, paulsz said:

oh okay, good to know. I did not know that. Thanks!

I asked ESV because there isn't any instructions regarding that nor any legitimate proof that you need hours apart for dosing.

[Clown79]

41 minutes ago, Hoosier said:

So my water change schedule has been 20% every 4 weeks (+/- 3 days).  If new water mixes up at a dKH = 10.5, and do a 20% change to a tank that is at dKH = 7.5, it should work out to an alkalinity of 8.1 after the water change.  Then I aim to hold that stable, until the next water change, at which point a 20% change should raise the dKH up to ~8.6, then aim to hold that stable, and so on, until I'm holding stable at the 10.5 the saltwater originially mixes up to.  Does that sound reasonable?

 

--Hoosier

If your salt mixes at 10.5, every time you do a water change, your tank should be reading pretty much the same when done regardless of volume of water changed. 

 

If you allow alk to drop in between waterchanges from the target level then you will see a significant difference.

 

Now if your salt doesn't mix to 10.5 and you dose to try to reach that target number, when you do a water change your levels will fluctuate.

 

That's why target levels should be based on what your salt mixes at and dosing in between waterchanges to maintain that target level.

 

 

[Hoosier]

19 hours ago, Clown79 said:

If your salt mixes at 10.5, every time you do a water change, your tank should be reading pretty much the same when done regardless of volume of water changed. 

 

 

It's been a long time since I had a chemistry class, but why wouldn't the resulting alkalinity be somewhere in-between the new water and the old water?

 

--Hoosier

[Hoosier]

19 hours ago, paulsz said:

you could also dose a bit to get it up to 10.5 over a few days, instead of waiting on water changes. 

 

note that you should also aim to have your cal and mag at the same level as your salt mix. Next time you make saltwater, test all three and write those down somewhere. That way you'll know to always aim for those. 

 

Ah, that's what I was trying to do, and it wasn't working.  At this point, I'm betting precipitation is the explanation, so I think I need to figure that out before I try again.

[paulsz]

9 minutes ago, Hoosier said:

It's been a long time since I had a chemistry class, but why wouldn't the resulting alkalinity be somewhere in-between the new water and the old water?

it will. What Clown79 was referring to is that if you bring your alkalinity up to 10.5 and have that set as a goal, every time you do a water change, it'll stay at 10.5. And whenever you dose, it's to get it back to 10.5. 

[Hoosier]

1 hour ago, paulsz said:

it will. What Clown79 was referring to is that if you bring your alkalinity up to 10.5 and have that set as a goal, every time you do a water change, it'll stay at 10.5. And whenever you dose, it's to get it back to 10.5. 

Cool.  That makes sense.  Thanks.

[Clown79]

1 hour ago, Hoosier said:

Cool.  That makes sense.  Thanks.

What I'm saying is, if you target your alk to what your salt mixes at rather than trying to increase it, there shouldn't be a change with waterchanges.

 

My salt mixes at 7.9-8.1 that's what I maintain.

When I do a waterchange and test my alk after, my alk is between 7.9-8.1 no major fluctuation.

 

If I wanted to maintain alk at 10 but my salt mixes at 8, every time I do a water change, it will change it won't stay at 10 because I'm adding saltwater with an alkalinity of 8.

 

So it's best and highly recommended to target your alk to what your salt mixes at and dose to maintain that.

 

Otherwise you are looking at fluctuations which is a major issue.

 

There is no need to have alk at 11 nor even 10.

Nsw is 7.  

[Hoosier]

Just an update to say thanks again, especially to Clown79 & paulsz.  After a month of just monitoring, I've concluded that my little reef community is consuming ~0.2 dKH worth of alkalinity per day.  This seems much more reasonable.  For now, my plan is to use dosing to maintain whatever it is after a water change, and let the water changes creep the target back up over a couple of months until it matches the freshly mixed saltwater.

 

I've also learned that I'm less likely to mess up with Salifert's alkalinity test than with Red Sea's, that for either one the range at which I think I'm at the end-color translates into a measurement error of about 0.2 dKh, and that I really need to wear my reading glasses to see the marks on the burets.