recently I bought a new tank, but the fish had been in it for a month maybe 6 weeks before they got sick. And the rest of the fish are fine. I try and clean out tank once a week but more often fortnightly. I remove about 1/4 of the water and replace it with rain water if i have collected enough. The only thing I can think I have done differently is that two weeks ago I went to the Animal Shack in Pukekohe and bought some fishy toys. I also purchased a package of tank stuff. It included, stress zyme, stress coat, ph test kit, and two packets of Electrolytes.
I added a packet of the Electrolytes to my water. That is the only thing i have done differen't in the last 7 months.
Regards
Kathy