I have a new aquarium (about 3 weeks old) that I am having trouble with. It is a 30 gallon tank with a whisper 30 filter and a whisper 60 air pump. Inside the tank are two decotration pieces (ships) that have fake plants. I followed all the directions for tank setup and waited about 3 days before adding 3 Platys. 2 days later 1 platy was dead. I cheacked water quality and had virtually no ammonia or nitrites. A week later I added a Green Tiger Barb. About 4 days later he started to get some white cottony looking stuff on him and looked like he was having trouble breathing. 2 days later I pulled him out and put him in a medicine tank and tried adding some anti-fungal treatment. He died that night. I then added 4 more Green Tiger Barbs. The next day they also started to get the white cottony looking stuff on them, stopped eating and became lethargic. I also noticed my lone Platy now too has white, cottonly substance on her, but she is still eating fine and staying active. I went ahead and medicated entire tank with anti-fungal, but 1 1/2 days days later all 4 new Green Tiger Barbs were dead. I just went ahead and did a 50% water change and added 6 more platys to the tank. Are they going to die also do you think? I've done 2-3 15% partial water changes since I got the tank, feed very lightly, and all my equipment seems to be functioning fine. What can I do? Thanks for your help!