My aquarium nitrates increase despite everything I am doing. I have a 20 gallon tank with a 20 gallon sump filled with biomedia, 5 gallon bucket filled with pumice with water going through at 50 Gph, 200ml purigen, carbon, 15 oz. Cobalt total nitrate, fluidized sand bed filter v2 bio600f, skimmer eheim hang on back for 100g+ tank, biopellet reactor, deep sand bed with sifting starfish, fluval 306, aquaclear 30, plus overflow/filter box from fluval 32 gallon glued inside 20. I add 100ml instant ocean nitrate reducer weekly, and yesterday added 7.5oz cobalt total nitrate resin. I fed about 20g tilapia yesterday after doing 7g water change with nitrate at 40ppm. Now they are at 60ppm. Despite 7g changes every other day I cannot keep nitrate under control at all. Nothing is eating and I'm surprised stuff hasn't died long ago. Can anyone see what I am doing wrong. The more I try the worse it gets. It's been running for 8+ months and never been this bad.