last week i noticed my 7" pbass appeared to have some type of fungus or fin rot. assuming this i started treating the water with melafix. today i picked up a nitrate test kit despite my local pet shop telling me i don't really need to test for nitrate? and my nitrate levels are HIGH! i have done a 25% water change. should i focus on lowering nitrate instead of treating the fish for what appears to be stress related injuries? what do you recommend? more water changes? if so how often? will changing my filter cartridges help? should i not change all the filter cartidges at once for fear of removing to much beneficial bacteria? i have a 55gallon with two emporer 400's with a 7" pbass, a 8" marbeled pim, and a silver dollar. any advice would be greatly appreciated!