I have a 12 gallon FOWLR I inherited with a clown, orchid DB and a goby pistol pair. Small CUC. I added a canister with Seachem matrix, purigen and an inline GFO reactor. Don't have space or budget for a sump et al. Also been adding Aquabella bacteria for a year. Phosphates were inline after the GFO as expected but nitrates stayed over 40-60. I change water once every 3 months and clean the canister every other water change. I can see the rolling eyeballs. Goal is to see how long I can go between water changes. Added a Santa Monica style ATS 2 months ago. Last week pre water change, no3 were <5ppm and po4 <.05. Next step is to remove the chemical media and GFO. Getting the experimentation out of the way before I get corals. I can't 100% attribute the low nutrients to the ATS but sure seems that way so far. Will observe for a while.