so my 5 inch sveni pike just died after 3 days of heavy breathing with his mouth stuck open. This has happened to several fish already but all my others are fine, but im assuming it must be a parasite or disease. My water params test perfect...ph 7.2, ammonia is 0, nitrates and nitrites are fine. The only other conclusion i can think of is i added some crushed coral to my tank to harden to water for a few dats i had, could this have been the cause? Ive decided i will probably do a complete overhaul, clean everything empty the tank completely and start from scratch. Does anyone have any other suggestions to avoid doing this?