The answer is both "yes" and "no".........would keeping some form of rock in freshwater create anaerobic bacteria that converted nitrate to nitrogen? This is the "yes" part. It will, technically, to some degree in the 02 depleted zones, but the stocking levels of most FW tanks make it very impractical to do so. This is the "no".....
If you kept very few fish in a tank filled with rock, you may close the gap a bit, but water changes and or plants are the most effective ways to nitrate reduction in a FW system. Deep sand beds can work pretty well, so theoretically yes you would create areas that would consume nitrate, but not enough to keep up with the production. Plants are very underrated in FW tanks but water changes are still necessary unless you had a heavily planted, lightly stocked tank. ......and then you would still need water changes for other reasons.
If you kept very few fish in a tank filled with rock, you may close the gap a bit, but water changes and or plants are the most effective ways to nitrate reduction in a FW system. Deep sand beds can work pretty well, so theoretically yes you would create areas that would consume nitrate, but not enough to keep up with the production. Plants are very underrated in FW tanks but water changes are still necessary unless you had a heavily planted, lightly stocked tank. ......and then you would still need water changes for other reasons.
