I could be wrong, but my thinking is that the system is limited by the diffusion of water down into the bed and the more surface area (top of the sand bed) the greater the amount of water that can diffuse down into it. Once you get to a certain depth, all of the NO3 is going to be consumed and it can do no more. You do need a certain depth but additional depth beyond that is of questionable value. I would much rather have more area for diffusion with a 3" bed than a small deep bed.
remote deep sand bed for no3/po4
- Thread starter davidwillis
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I have long posted that sand beds as time bombs is one of the horrible myths of modern reef keeping. A massive amount of sand can mask the need to remove phosphate for quite some time, but that is a product of the reefer not knowing their craft and not an issue with the sand bed it's self - eventually the sand cannot do any more work and that cannot be the hobbyists fault that phosphates start to rise quickly, right? 
For denitrification, the sand could fill up with that inert grey sludge that gets into sumps and stuff - I do advocate cleaning it out of sand beds every 4 years, or so, and I supposed that rinsing a bucket every few years can do the same thing.
Most people with remote DSBs just replace the sand, though.
Diffusion can be accounted for by more flow. Nobody knows if the water that enters the sandbed has 100% of the no3 removed, or 1%. Maybe less flow would yield a larger percentage drop whereas more flow would be less. In the end, the bacteria is going to multiply to handle as much as it can. I once had a large FOWLR of about 450 gallons that was loaded with huge fish that ate a ton. I had that Carib Sea Sea Floor which was larger shells and stuff since the fish would move around the sand constantly. I had a 75g fuge on this tank with just a bit of macro that grew mysid shrimp (not enough macro to do much) but it had a 4-5 inch sandbed. This smaller area kept the no3 for this whole system barelty detectable which really was a problem since the coralline grew like crazy in the display and some of these fish liked to see if my arm tasted good. In the end, surface area might matter, but my guess is that unless the surface area is saturated with bacteria, there is plenty of room for smaller areas to do more work with more concentrated populations.
For denitrification, the sand could fill up with that inert grey sludge that gets into sumps and stuff - I do advocate cleaning it out of sand beds every 4 years, or so, and I supposed that rinsing a bucket every few years can do the same thing.Most people with remote DSBs just replace the sand, though.
Diffusion can be accounted for by more flow. Nobody knows if the water that enters the sandbed has 100% of the no3 removed, or 1%. Maybe less flow would yield a larger percentage drop whereas more flow would be less. In the end, the bacteria is going to multiply to handle as much as it can. I once had a large FOWLR of about 450 gallons that was loaded with huge fish that ate a ton. I had that Carib Sea Sea Floor which was larger shells and stuff since the fish would move around the sand constantly. I had a 75g fuge on this tank with just a bit of macro that grew mysid shrimp (not enough macro to do much) but it had a 4-5 inch sandbed. This smaller area kept the no3 for this whole system barelty detectable which really was a problem since the coralline grew like crazy in the display and some of these fish liked to see if my arm tasted good. In the end, surface area might matter, but my guess is that unless the surface area is saturated with bacteria, there is plenty of room for smaller areas to do more work with more concentrated populations.
Dburr1014
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How is this test going?
I'm very curious.
I had just removed my very small sand bed a couple weeks ago. 5" in a 5 gallon. To my surprise, no3 11.5 ppm after a year of zeros on my hanna test kit. Po4 2.1 (testing again when I get home) after years of 0.1.
Cyano outbreak in my display and refuge. Cheato getting wilty. Burnt tips on my valida.
I may have undone what was working so nicely in my system.
I'm very curious.
I had just removed my very small sand bed a couple weeks ago. 5" in a 5 gallon. To my surprise, no3 11.5 ppm after a year of zeros on my hanna test kit. Po4 2.1 (testing again when I get home) after years of 0.1.
Cyano outbreak in my display and refuge. Cheato getting wilty. Burnt tips on my valida.
I may have undone what was working so nicely in my system.
davidwillis
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I have not tested in a few weeks, but last I tested no3 was staying about 20. I use LC to keep the po4 down. Before that I was up to 8.0 on po4 (not 0.8, and not 0.08, but 8.0). I will run LC once po4 gets up to 0.15, and bring it down to 0.1 in about a week or two if dripping it into a reactor (with a 5 mocron filter on the output). Maybe at some point I won't need to us LC if the Deep sand bed keeps it down, but I didn't start the deep sand bed for po4. Cheato and turf scrubbers could not keep po4 or nitrate under control in my tank.
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