My tank has been up for about 4 months now. Added 3 chromis to start then after 2 weeks added 2 ocelaris clowns, then added a kole tang and a purple psuedo. Tank is 75 gallon with 30 sump fuge. All fish eating acting normal. Tang was eating half a sheet of nori a day but would not touch any other food. No qt on any fish, I know I should know better.. Tang was first to go looked fine eating then bam next day dead. Next dumb mistake, freshly hatched brine I accidentally put in a bowl tht was dirty with who knows a little soap a little hamburger grease. Did not realize it till after.. So threw carbon in changed 5 gallons of water. Next day chromis dead and psuedo dead eating fine night before. Clowns at bottom of tank changed 8 gallons tht day. Clowns remain at bottom but swimming to eat look fine. Today find clowns dead;( have some more water ready to change.. 1 chromis left eats looks fine. Corals are fine and snails. Weird thing Nass snais will not touch these dead fish. Disease? Or my stuidity? Params as follows- amm 0, trite 0, ph 8.1, trate 0, calc 480. Starting to get cyano so I know phosphate is there. Any ideas would be greatly appreciated.