have you been changing your canister media?
I know they can become nitrate factories if not properly kept up with.
Have you thought about adding a sump and skimmer/fuge setup?
If not you may want to consider doing some mangroves or some kind of macroalgae in your display tank, they can help offset high nitrates _________ 
24G JBJ Nano, 20# Live Sand, 40# Live Rock
Rose BTA, Kenya Tree, Frogspawn, Xenia, Shrooms, Green Candy Cane, Duncans
Blue/Green Chromis, 2x Black & White Percs, Dragon Goby, Six Line Wrasse, Mandarin Dragonette
58G Oceanic, 60# LS, 60 LR, Lots of goodies 
Up and coming 90g stay tuned  |