hey all i have just lost my huge red tail to an unknown reason. last night after acting fine as long as i can remember he started laying sideways and then belly up. i tested everything really quick as soon as he started acting funny and changed 30% of water just to be safe. last night and with no astronomically hard levels, he still passed on. he was around 8 years old, 20-24 inches and eating feeders once a week, pellets and shrimp the rest. now as of today, my other huge cat is doing the same. after being fine last night and this am. i went to work this after noon he was swimming, the water levels were good at 0-.25 ammonia, same exact with nitrite, 7.9 PH and the nitrates under 5.0. i also have been using prime with every change to balance anything out. this really sucks there my stars that everyone including me love and now im going to lose the other 26 inch one. also just in case anyone asks i am running a 200 gallon canister filter with UV and a 400 gph hanger on the back with a scrubber for all contaminates as a little boost on a 180 gallon. please help before i loose any more cats! im almost done making them a 1500 gallon in the basement and in a few weeks there new home, i really really do not want to loose any more.