65gal of water. With reactors, sump, protein skimmer. Tank has been running 15 months. The water was perfect before I added 2 1" clowns, A 2" mandarin gobie, a 2" coral beauty. After I added these fish one clown died at 3 days, the second clown died a week later. Coral beauty and mandarin are still alive. First clown couldn't be found, I couldn't find the second. Ammonia was reading .50 ppm just as the second clown died. Do you think it was a mistake introducing these four fish at one time? Or is there another issue with my tank?