I have a 65g tank with about 57g of water, a 1.5 - 2 inch sandbed. 2 clowns and 1 midas blenny. 3 blue leg hermits 1 emerald crab 1 conch 2 trochus 5 nassarius 5 cerith. I have 7 coral frags. I started the tank April of last year so just over a year ago. I run a canister filter and that isn't going to change. My problem is nitrates. I was doing 10g wc a week with saltwater from fish store. I have tested their water a few times and it's never even been 5ppm nitrate. My nitrates got up to at least 50 ( that's the highest my red sea test goes) so I started doing 20g weekly wc for about 3 months to get it down to about 5. I also added 1.5 bottles of matrix to canister filter (that's 3x what the bottle says for my tank) I also removed all mechanical filters except a 1/4 inch thick piece of filter ( I buy it at Walmart it's quilt batting) I change it out every other day. I have always cleaned canister out every week including propeller and I clean hoses about once a month. I don't over feed. I only feed every other day and nothing reaches the sandbed. I have tried blowing off rock a section every wc. Once the nitrates were a 5ppm I went back to 10g wc a week and of course the nitrates started going back up and within a month maybe less the nitrates back to 50ppm. I don't know what else to do. I can't keep doing 20g wc weekly. I don't want to get any more fish because that is just going to make it worse. Someone please help.