I have bumped up my water changes to two 50% a week and I can keep my nitrates at abotu 15 - 20. This is because my water tap has nitrates in it, I know that products that clam to remove nitrates don't work all that will, but could they help prefilter my tap water? I bought an R/O and it didn't remove the nitrates, possible due to lack of water pressure going into the unit, or cheap membrane.