I have a 55 gal saltwater tank that has been set up since July. I am currently running a fluval 406 canister with Phosguard, carbon and chemipure. I also have a sea clone HOB skimmer that I empty 1-2 times a week. Skim mate is very dark. My sg is 1.024 am 0 trite 0 trate 0 kh 12 ph 8.2 temp 79 phosphate .5 calcium 440. 2 months ago all my fish died. They were in the tank for 3 months very happy and healthy. All died at one time overnight. They were a small yellow tang, coral beauty, 2 pajama cardinals. I did. 50% WC and let it sit for a month running the filters. Added 3 green chromis, all died within 24 hours. Went to my LFS and explained the situation, they said do another water change then add a hearty fish.. This weekend I bought another coral beauty, died within 6 hours. I do have coral, rhodactis mushroom, fine grape , a colony of plays, pulsing Xenia and a colony of zoos. They are all thriving, however the zoos have only been opening halfway. Does anyone have any suggestions on how I can fix or what the problem may be? I am running 2 x 54w t5 HO bulbs one actinic and one Ocean Sun.