Yet Another Lr Question

[Donya]

Given a tank of say, 10 gallons, that would be 10lbs LR by the "general rule", and that will support X amount of biomass. Supposing the water volume was then increased somehow to 20 gallons, the general rule would stipulate more LR needed. But, hypothetically speaking, wouldn't the same amount of LR be able to support the same amount of fish regardless of the size of the environment? With sufficient water turnover, would 10lbs of LR be able to support a 2" fish in a swimming pool volume of water, or would the waste be so dilute that the rocks' bacteria would die back from the levels they would be at in a 10 gallon tank?

I figure I either just asked something that should be blatently obvious to me, or I need to stop staying up at night pondering this sort of stuff.

 

[SkiFletch]

I think you're refferring to adding a sump for the extra water capacity? In theory, yes what you propose is true, 10lbs of LR should be able to support a nano 10gal tank, but most nano owners would advise you to go with 15lbs of LR for a tank volume that small

 

[Donya]

It's not really a specific case I'm wondering about, just the effects of water volume on a given amount of LR's ability to filter effectively. If the LR can filter for a given environment and the water volume is suddenly increased a lot while the amount of biomass is left unchanged, the nutrient concentration in the water would drop...making me wonder if LR's filtering efficiency is affected by nutrient concentration, even though the actual number of molecules being produced by animals would be no different.

Mainly I'm considering that if concentration is a factor, I want to try some experiments with it (suff-in-a-jar type experiments, not anything with tank beasties involved).

 

[Mr Miagi]

Bacteria and microbial life found on LR would be dependent on the concentration of nutrients. Its food for growth and reproduction for them. Why would you want to run experiments on this kind of thing? (Dont men to sound harsh, just want to know what your going to gain from the experiment?).

Each tank is structured differently, has different LR, bioloads, feeding habits, additives vary etc etc too many other conditions found in reef tanks that could play a role in how effective LR is, and none which you could account for.

You might have to deffine your guiding question (hypothesis) for your experiment alot more.

 

[Aquascaper]

If water volume is increased but the amount of live rock is constant then I would suggest that water circulation is increased to compensate.

 

[Donya]

If concentration is the key and current can compensate by maintaining encounter rate, then there must be a point at which the current can become too high for the system to function...in which case the hypothetical situation of 10lbs LR and one small fish in a swimming pool would probably fail. There was something about it that just seemed intuitively like it wouldn't work, but I wasn't sure.

I'm not sure exactly what experiments I would be running, or have the ability to run yet. I would find it interesting to take a set gph and small chunk of rock and see exactly what happens to chemical levels if I supply a constant rate of ammonia or other nutrients somehow, but then increase the water volume dramatically after a while (maybe nitrite is the first one to show up in excess for example). I realize there would be variation in the rock, but with multiple pieces taken from different sources kept under the same conditions, it would (hopefully) show a general trend of some sort. As far as what I would gain from the experiment...the satisfaction of knowing bacteria's response to the situation described I'm one of those people who can't leave niggling little gaps in information alone until I know the answer

 

[Aquascaper]

If concentration is the key and current can compensate by maintaining encounter rate, then there must be a point at which the current can become too high for the system to function

There would be a point at which the water flow through the live rock would be too great to allow the bacteria sufficient exposure to the compounds but this would be impossible the reach in an aquarium as natural flow rates on a reef are huge IMO

 

[pleder]

I think it would be fine. the LR is not the filter. The bacteria on the liverock is. If the bacteria colonies were capable of supporting the bioload of a system then it should be constant regardless of the water quantity.

The 1lbs per gallon is a rule of thumb. They are the simple rules that most can understand without further explanation. There is theory behind them.

 

[Donya]

There would be a point at which the water flow through the live rock would be too great to allow the bacteria sufficient exposure to the compounds but this would be impossible the reach in an aquarium as natural flow rates on a reef are huge IMO

Do you mean huge because of the volume of new water being passed over, or the speed at which the water is moving relative to stationary objects? I'm a bit confused by which you meant. If I were to put 200x gph on 5 gallons, it would turn into froth and not much could live in there I don't think...

If the bacteria colonies were capable of supporting the bioload of a system then it should be constant regardless of the water quantity.

True, but encounter rate is important. If you have X nutrient molecules in A gallons of water, if the same system is suddenly put into 2A gallons of water then the concentration of nutrients is X/2A rather than X/A. So, with the same turnover rate, the bacteria would be exposed to 1/2 the nutrients per unit time with 2A volume. Crank up the flow rate and the exposure will then be the same in 2A water (unless the rate is too high for encounters to happen).

They are the simple rules that most can understand without further explanation. There is theory behind them.

I realize that, but the reasons for that theory are important (and not all general rules are correct...not saying this one isn't, but I prefer not to take things for granted). I'm sure there are reasons that 1lb per gallon tends to work, but it's the exact mechanisms of why that is the case that I'm interested in.

 

[Aquascaper]

There would be a point at which the water flow through the live rock would be too great to allow the bacteria sufficient exposure to the compounds but this would be impossible the reach in an aquarium as natural flow rates on a reef are huge IMO

Do you mean huge because of the volume of new water being passed over, or the speed at which the water is moving relative to stationary objects? I'm a bit confused by which you meant. If I were to put 200x gph on 5 gallons, it would turn into froth and not much could live in there I don't think...

The volume of water as well as flow rate is huge that is why it is impossible to recreate in an aquarium.

As you righlty pointed out if you setup a flow rate of x200 on a 5g the water would soon leave the tank and be on the floor but that still only represents a rate of 100gph (3785lph) - My 120g tank had a flow rate of over x90, over 3000gph (11000lph) and this barely had an effect and is only half what you've suggested (x200)

From what I can research (which has been very limited) natural reefs can have flow rates in the regions of 10,000gph (38,000lph) - a very approximate figure. If you convert this into a tank size using the minimum guide level of x20 tank volume for the lph flow rate:

38000lph (flow rate) divided by 20 (tank volumes) to get tank volume = 1900g

As you can see it is possible to achieve but, in terms of the average aquarist, a 1900g tank is imposible to achieve.

HTH in some way

 

[Donya]

That helps a lot! Thanks Aquascaper