Hi Guys I have A 50 gallon salt tank had it up cycling for 4 and a half months and finally decided to add a fish my choice was the damsel since i heard they were hardy fish. But 5 days later he began to show signs of ill and died the next day. Im I doing something wrong? adding fish to early? i had it up for 4 months have heater filter and skimmer live sand rocks everything. can somebody help me?