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Crys

Granite as live rock?

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Crys

When I first set up my tank the live rock I was sold was a piece of granite,  I also got two pieces of dry rock (reclaimed coral). It has been over a year and the dry is now live. My question is, am I losing goid biological filtration or lack of minerals by having a large part of my rock granite.  I have a 13.5 gal and half the rock is granite. 

Thanks

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OldManSea

Granite has no real openings to allow microbe growth.  You only get some on the surface.  Coral based rock has enormous surface area with all of its nooks and crannies. You do sacrifice considerable biological filtration with the granite.

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jservedio

Granite will hold slightly more bacteria than your glass, which is to say basically none at all. Put it out in your garden or use it as a door stop and buy yourself some calcium carbonate rock. It's the backbone of your filtration.

 

If you really want it for scape purposes, you'll need some real rock or other biological media to house all that bacteria. If it's your first reef, it'll make things harder and more complex than they already are - best to start properly.

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DSA65PRO

I have Black Granite Counter tops in my Bathrooms. They are slightly magnetic, Also a magnet will stick to them. So it would seem they have Metal in them. BTW I Found out about the Magnetism when I dropped a paper clip and couldn’t find it. It was stuck to the underside of the edge. 
 

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Tamberav

I have solid 'rocks' in my cold water tank but it's because thats how the rock looks in the pacific. It makes the tank more difficult to manage and I don't recommend it for a tropical reef tank. 

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Tired

You should absolutely get some good coral rock. Now that your dry rock is decently colonized, you can safely replace the granite with something else. Granite is pretty, but provides basically no biological filtration benefit. I like it in freshwater tanks. though. 

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seabass
4 hours ago, Crys said:

It has been over a year and the dry is now live.

What the others have said is not wrong, and are reasonable arguments for using (or starting with) porous calcium carbonate rock.  You might even add pH buffering as a potential advantage when using calcium based rock.  However, it's been a year, and obviously your tank has a working biofilter or you'd be having problems.

 

It's amazing how the nitrifying bacteria get established on anything solid.  I totally get the surface area argument of porous rock (and sand).  But if we consider how much surface area is lost when of a piece of porous rock becomes heavily encrusted with coralline algae, we begin to see that less porous rock might still be adequate.

 

That said, your less porous rock might not have the same potential as a more porous alternative.  However, unless you are planning a substantial increase in your tank's bio-load, I wouldn't worry about it too much.  And if you are using aragonite sand, that should help provide some buffering capabilities (and surface area).

 

3 hours ago, DSA65PRO said:

I have Black Granite Counter tops in my Bathrooms. They are slightly magnetic,

I suppose the different colors in the rock potentially have different mineral and metallic properties.  While this unknown make-up of the rock might be problematic, it should basically be mostly inert.  Crys, I wouldn't be overly concerned if I were you; quartz and granite are usually considered reef safe materials.

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Crys

Thanks for all your help. I do have trouble keeping calcium levels high enough, and phosphates are around 0 most of the time. Would replacing the granite help improve those numbers? I wondered if the calcium based rocks helped with calcium retention. 

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seabass
35 minutes ago, Crys said:

I do have trouble keeping calcium levels high enough, and phosphates are around 0 most of the time. Would replacing the granite help improve those numbers? I wondered if the calcium based rocks helped with calcium retention. 

I wouldn't think that changing your rock would affect levels very much.  You'd probably be better off with changing to a salt mix with higher calcium levels, or by starting to dose two part solution.

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mcarroll
On 9/11/2020 at 2:15 AM, seabass said:

It's amazing how the nitrifying bacteria get established on anything solid.  I totally get the surface area argument of porous rock (and sand).  But if we consider how much surface area is lost when of a piece of porous rock becomes heavily encrusted with coralline algae, we begin to see that less porous rock might still be adequate.

Could be the denitrification is impacted more than ammonia processing.   👍

 

 

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seabass
1 hour ago, mcarroll said:

Could be the denitrification is impacted more than ammonia processing.

I'm fairly convinced that rock doesn't support denitrification as well as a deep sand bed (or remote deep sand bed).  I keep a couple of Brute containers full of live rock (one even has a 40 lb rock in it, but most are closer to 10 lbs).  I keep the nitrifying bacteria alive by occasionally dosing ammonium chloride.  But even when I'm not dosing ammonium chloride, I detect relatively high nitrate levels.  Maybe someday I'll do a series of tests to see at what level (if any) of denitrification actually takes place.

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mcarroll
2 hours ago, seabass said:

I'm fairly convinced that rock doesn't support denitrification as well as a deep sand bed (or remote deep sand bed).

Could be.  But I wonder if the primary limits are related to substrate?

 

2 hours ago, seabass said:

I keep a couple of Brute containers full of live rock (one even has a 40 lb rock in it, but most are closer to 10 lbs).  I keep the nitrifying bacteria alive by occasionally dosing ammonium chloride.  But even when I'm not dosing ammonium chloride, I detect relatively high nitrate levels.  Maybe someday I'll do a series of tests to see at what level (if any) of denitrification actually takes place.

That might be a pretty un-dynamic and un-reef-like setup, so maybe not entirely surprising.  

 

Unless it's got the strong flow AND strong aeration of a reef and maybe a complete food input, carbon limitation would be my first guess...maybe among other limits.

 

Especially so since the system has been jacked up with nitrogen (ammonia), leading other factors (like carbon) to depletion.  Of course that's speculation on the scanty evidence I have so far....could be plain wrong and/or there could be other significant factors!  😉  (But this is one reason I'm not a huge fan of ammonia starts for new tanks for new reefers.  Nitrogen eutrophication isn't the state under which you'd ideally want to start a reef tank...even if it works fine for starting a bio-filter.)

 

 

 

Wow...I just hit Google with "denitrfication on marine substrate" and got this PDF hit:

https://www.researchgate.net/profile/Qiaochong_He/publication/325015466_Biological_denitrification_in_marine_aquaculture_systems_A_multiple_electron_donor_microcosm_study/links/5af5fccba6fdcc0c030c5a73/Biological-denitrification-in-marine-aquaculture-systems-A-multiple-electron-donor-microcosm-study.pdf

 

Here's the abstract, but click over and read the whole article if you can (innocent bystanders: an aquarium is one kind of RAS):

Quote

There is a lack of information on denitrification of saline wastewaters, such as those from marine recirculating aquaculture systems (RAS), ion exchange brines and wastewater in areas where sea water is used for toiletflushing. In this study, side-by-side microcosms were used to compare methanol, fish waste (FW), wood chips, elemental sulfur (S0) and a combination of wood chips and sulfur for saline wastewater denitrification. The highest denitrification rate was obtained with methanol (23.4 g N/(m3·d)), followed by FW (4.5 g N/(m3·d)), S0 (3.5 g N/(m3·d)), eucalyptus mulch (2.6 g N/(m3·d)), and eucalyptus mulch with sulfur (2.2 g N/(m3·d)). Significant differences were observed in denitrification rate for different wood species (pine > oak≫eucalyptus) due to differences in readily biodegradable organic carbon released. A pine wood-sulfur heterotrophic-autotrophic denitrification (P-WSHAD) process provided a high denitrification rate (7.2–11.9 g N/ (m3·d)), with lower alkalinity consumption and sulfate generation than sulfur alone.

It's not in the abstract, but they pretty much lay out, in denitrification terms, why folks shouldn't carbon dose their tanks willy nilly...among lots of other cool info!  

 

 

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