[Sk8r]

Change water at least 30%.
Run carbon.
I'm suspecting the validity of this test...run it again. If you still have corals, they're a miracle.
Filters must be changed weekly. Cannisters are good at causing a nitrate rise: so is a crushed coral substrate. If you have corals you should have 1 lb live rock per gallon---55 to 60 lbs. How much live rock have you got?

I'm hating the amount of omg news I'm delivering here, but this is the hard way to do a reef. If it were mine---I'd pull everybody to quarantine, pull the live rock there too; totally pull the sandbed, in favor of buying aragonite fine grade, immediately replace the live rock , add the washed aragonite sand, and wait for a cycle, feeding tank 3 flakes of fish food daily---cycle which should be real fast, like a week. Then when you've spiked a tiny bit of ammonia and settled again to 0 nitrate, 0 ammonia, add a cleaning crew, about 20 snails, 10 scarlet hermits. AND NO FILTER at all. Trust your skimmer and your sandbed. An aragonite sandbed is a lot more potent at reducing waste and breaking down nitrates.

After that, you should run without ammonia or nitrate at all, certainly no higher than 3. You have 2 major nitrate generators in your current tank, in that uncleaned cannister and your cc sandbed, and if you can rid yourself of those, you will solve your problem---much work as it may be now, it will save you a world of frustration.