I just got a 16 gallon freshwater tank for my son with the glo fish. Two batches of glo fish have since died. Checked the water for ph, nitrates and ammonia no problems - even took a sample of the water to Petco , they check and no problems with the water. What is happening? Pump is running - I let the tank cycle for 24 hours. Yes, I added water conditioner. Never had this happen before any ideas? 
