a True DSB should be 4inches deep. Killer is right denitrifying bacteria is anerobic but that bacteria is located in the lower inch to two inches of a 4inch dsb. In my research flow rates dont matter if you have the right amount of substrate. As long as the sand is undisturbed, that is the key. If you have snails and other critters that will dig down deep to the sand bed that willl aerate the dsb and defeat the purpose. The other thing too is that higher flow rates arent proportional to the amount of dissolved oxygen, the distruption of the surface of the water is what causes the introduction of oxygen into water. You can have a tank with 6 powerheads whipping water and sand all over the tank but if your not causing the water surface to break then your not introducing oxygen. Along a river, when the rushing water tumbles over a waterfalls that introduces oxygen into the river. Just like when water in our sumps goes over a baffle.
Thanks guys. I had a DSB in one of my tanks many years ago but changed to no sand at all for the past 6 years with good success. I working on an upgrade which will be more than 100gls over what i'm currently running, so i thought about giving the Remote DSB a try. Thanks again for your knowledge. Mr.S.