Lowering Nitrates

[Randy Holmes-Farley Verified Community Expert]

When carbon dosing one must keep in mind that there is roughly a 16:1 / nitrate: phosphate reduction. Basically, when your phosphate level drops to undetectable levels your nitrates will not drop anymore. To reduce nitrates further one would either have to look for a chemical route to drop it or do some water changes. Also sometimes nitrate and phosphates in live rock can leech back into the water.

It actually can be more extreme than 16:1 if any significant amount of the nitrate is being consumed in low O2 areas (like in the sand or live rock pores) where it is also used instead of oxygen as an electron acceptor, producing N2, instead of just as a source of nitrogen atoms to build tissue.