Denitrifying quality of live rock?

[UrbanSage]

Hi all,

I am under the impression that I some time ago came across a study into the denitrifying ability of live rock.
I seem to recall that the study found that although anaerobic conditions do produce nitrogen from nitrate the process is not impacting on aquariums due to limited size of aquariums, wrong flow, or something else.

Does anyone know what I am talking about or even know enough to tell me I am dead wrong in thinking this?

Thanks!

 

[xJake]

Check out this article:
http://reefkeeping.com/issues/2004-05/rs/feature/index.php

 

[UrbanSage]

Thanks, it is some of the information I have dug out as well. There is a good discussion in Shimek's reefkeeping forum and I think the bits and pieces collected various places is what is grounds for my current perception.

Thanks again!

 

[wayne in norway]

I find it pretty difficult to believe that the 'porous' interior of live rock is a fantastic site for massive amounts of denitrafication. I think the better story is that it happens in biofilms on surfaces exposed to the tank water. You can pick holes on transporting nitrate into the rock, the amount of permeability of the rock (more important than porosity, what if the pores are not connected, blocked, the case in most biogenic limestones?) and transport of nitrogen gas out of the rock. The biofilm story just seems to pass Occam's razor a bit more credibly. Theres some stuff in Delbeek and Sprung vol 3 with references.

When you start to think about this you start to see the mechanisms and reasons why sand beds are going to be so much better at denitrafication - it is so much easier to move nitrate laden water thro' the sand bed by diffusion, advection and biological processes, and easier to get it out, and the surface area for bacteral residnce would seem to be higher.

Ron of course likes sand beds, but seems to think think that biological action is the main driver for moving water and wastes thro' the sandbed, correctly dismissing diffusion as a weak process, but ignoring advection. Huettels paper of 1996 is a good counterpoint, and an interesting read - using a tank simulation a current alone moved pieces of neutral density acrylic a few cms into a sand bed after only 10 hours. Seems a good reason to keep water velocity over those sand beds up pretty high. Rusch and Huettel 2000 in Limnology and Oceanography is also a valuable read on the subject of sandbeds.

 

[Paul B]

I believe that rock, if you have enough is all that is needed in a tank to control nitrates. I can only go by my experiences as I don't know how old Sprung and Delbeeks tanks are (but I do remember when they started) or where Ron got his information from. In my tank anyway, my nitrates read close to zero, my tank is very heavy on fish which are fed a lot due to breeding experiments. I only have rock for denitrification and a RUGF. The tank is close to 40 years old. The nitrates have to be going someplace.

 

[rivoth]

You could always set up an experiment. Take two 10 gallon tanks. In one you put a typical large sized chunk of well cured live rock and a 20x to 40x circulation pump. In the other you attach an active biowheel filter. Block both tanks off completely from light sources so algae cannot grow.

Run a small and equal NH4 drip into both tanks and regularly measure N03, NO2 and NH4 levels. See if you can make the NH4 drip be equivalent to what you would expect from feeding a few fish. The NH4 and NO2 tests will confirm that both systems are keeping up with the simulated bio load.

The biowheel tank should convert the NH4 to NO3 and go no farther. The live rock tank will do the same with the possibility of additional N03 denitrification. Let the experiment run at least eight months since the denitrification bacteria takes a lot longer to get established.

The comparison of the difference in NO3 levels should give you a measure of how much denitrification is being done by the live rock. I think this experiment will tell you if the live rock produces useful levels of denitrification. If the live rock tank NO3 levels reach a plateau then you can try raising the NH4 drip rates.

 

[demonsp]

Lr will convert nitrate and ammonia into nitrogen in proper conditions and flow is high on that list. Same with the SB. But its not just the LR , its also the pods and unseen bacteria that all over the rock. It might be safe to say its what you cant see that matters.
But if the load is greater then the amount they can control then you see problems.

 

[kmckay]

If LR doesn't work, then how do all of the bare bottom tanks achieve nitrate control?

 

[wayne in norway]

Not all of them do. It was, as I recall, a problem with older berlin type systems. And I'm not saying it doesn't do anything, I jsut don't believe it's as good as people are sometimes told that it is, and that leads to overexpectation. And I believe it does it near the surface of the rock, not buried deep inside.
Big skimmer, and a low fish load helps too.

There are few definites in aquarium filtration. You need a balance based on reality

 

[RicksReefs]

but what if my reality differs from your reality?

 

[UrbanSage]

What does the sea monkey on your back think about your reality?

I'm sure live rock provides denitrification to some extend.
But does it have anything to do with the oxygen poor core or is it simply algae/bacteria covering the rock?

 

[RicksReefs]

the seamonkey said his reality thought we settled this 15-20 years ago.

 

[norskfisk]

Forgive me my newbie style here. I wasn't around the hobby 15-20 years ago. I tend to like the idea that live rock and live sand don't do that much in terms of denitrification, though I am not entirely convinced about it. But it's just so hard to believe that the nitrate gets in/down there. I mean it's a dead end road so what's it doing there? I prefer the theory that the food is immediately eaten by animals in the LR/LS, then the wastes that reach inorganic state before being skimmed out go into algae. This is again eaten by grazers either introduced or in the LR/LS. Then a new portion is skimmed out. Thus you get this exponential "halving time" that tells how much remains in the system after a certain time. Amount of algae stabilizes after awhile when nutrient import grazing pressure is constant. With the very high metabolic rates in tropical environments this could remove all nutrients pretty fast. So all nitrate is removed by algae, nothing by denitrification. Just a thought.

 

[billsreef]

<a href=showthread.php?s=&postid=12667836#post12667836 target=_blank>Originally posted</a> by wayne in norway
I think the better story is that it happens in biofilms on surfaces exposed to the tank water.

:thumbsup:

There's a lot of N hungry life on the surfaces of LR. Additionally, Dr. Timothy Hovenac has looked for bacteria in and on LR. He didn't find any in the core of the LR, so it's pretty hard to figure on any bacteria breaking done NO3 in the core of the rock There also is a lot of algae in the surface 1" of any sand bed that consumes some of the NO3. The advection also is a strong transport method that does indeed work tank water and detritus done into the depths of the sand bed where bacteria can work on it

BTW, my monkey says there is no reality :eek1:

 

[Paul B]

Forgive me my newbie style here. I wasn't around the hobby 15-20 years ago. I tend to like the idea that live rock and live sand don't do that much in terms of denitrification, though I am not entirely convinced about it. But it's just so hard to believe that the nitrate gets in/down there. I mean it's a dead end road so what's it doing there? I prefer the theory that the food is immediately eaten by animals in the LR/LS, then the wastes that reach inorganic state before being skimmed out go into algae. This is again eaten by grazers either introduced or in the LR/LS. Then a new portion is skimmed out. Thus you get this exponential "halving time" that tells how much remains in the system after a certain time. Amount of algae stabilizes after awhile when nutrient import grazing pressure is constant. With the very high metabolic rates in tropical environments this could remove all nutrients pretty fast. So all nitrate is removed by algae, nothing by denitrification. Just a thought.

Actually nitrate disappears even if there is no skimmer it just would build up faster without one. Animals eating the food also do not remove much nitrate although there are bacteria in the gut of animals which probably convert some of it. Algae also consume nitrate but unless the algae is removed from the tank, it stays there until the algae dies and releases the nitrate.
I change very little water and I have not harvested algae in about a year, I have almost zero nitrates. My tank is heavily fed due to breeding experiments and too many animals but the nitrates are going someplace. I also don't have a DSB so the nitrates must be processed in the rock.

 

[Randy Holmes-Farley]

But it's just so hard to believe that the nitrate gets in/down there.

Nevertheless, it can happen in sand, and has been demonstrated in test tanks with little more than sand in them. I believe Rob Toonen showed this. It can also be seen indirectly in some tanks where bubbles that are presumably N2 are readily found below the surface.

 

[wayne in norway]

But it's just so hard to believe that the nitrate gets in/down there.

It's pretty easy to get detritus and any dissolved materials into sand beds - that's been well demonstrated in experimental setups, and goes faster than you'd imagine with a nice brisk flow of water. Getting it in and out of rocks is not so easy - there are plenty of roadblocks to explaining that, or at least explaining it in a way that allows for transport in and out to happen at a rate that is useful to us. We've all seen the photos of pieces of LR that have been sliced and show a dark low O zone in the middle with a surface layer that's brighter in colour. That's great, but it doesn't tell you how long it took for that situation to be arrived at. If you were to make some cubes of LR, and submerge them in a sump, you could pull them out and see how long it took for a colour pattern like to this to form.

 

[Randy Holmes-Farley]

But it's just so hard to believe that the nitrate gets in/down there.

In sand? Why is that hard to believe?

I agree that for live rock the situation may be different, and the amount of denitrification that takes place, if any, will vary tremendously with the nature of the rocks itself, and may often not be important on the scale of a reef aquarium. But I'll note that even in Ron Shimek's discussion of denitrification in live rock (linked above), which I find unconvincing, by the way, he claims that algae thrive inside of live rock.

So to my way of thinking, if algae can thrive inside of the rock, there is adequate transport of dissolved ions to the algae to let it live. I'd propose that the same transport would happen if that algae died and was replaced by bacteria. I don't know why Ron would make the assumption that transport must necessarily be slow if algae do grow there, but he and I often do not see eye to eye on science.

 

[norskfisk]

Well, the question is how much denitrification contributes to the overall export of nitrogen.

A sandbed where denitrification takes place must be somewhat stagnant. Perhaps very stagnant for it to take place to a significant degree. So this sandbed is so stagnant that oxygen is very limited down there, but food particles get down there and find their way between the sand particles without any current to lead them. And significant amounts of nitrogen from the water column makes it down there too. I am just asking if it is safe to assume that this must be the way it happens when there are competing theories.

 

[UrbanSage]

Competing theories regarding sand beds?

It doesn't have to be any more stagnant than a nitrate filter where water trickles through

With the amount of gas being released I would assume there is quite a bit of micro movement in a sand bed. (Not even talking about life in the sand).

In a rock however I don't see bubbles forcing their way to the surface and create movement in the surrounding matter in doing so.