Airyshone

Hi there, i have a curious problem. I had two fish for the last year, a shub and a mocha fantail. They had had quite a bit of trouble with fin rot over the summer, but were on the mend so i moved them from my parents house in tauranga to hamilton. Now the trouble began. They were fine for almost a month, then all of a sudden one morning they both have dropsy. Inevitably they died. I cleaned the tank top to bottom, let it dry out for two weeks, then got two new fish, a shub fantail and a red comet. This time i wasn't going to let them get dropsy so i invested in a good quality filter. However, i discovered yesterday that the shub fantail has dropsy, i immediately removed him from the tank. And this morning, the comet's scales started to stick out, although it hasn't increased in size. I have only had these fish for a week and a half, and am puzzled as to what is causing it. The only thing i can think of is that there is something in the water that the filter isn't removing that is causing this. Has anyone else had any trouble? Just to be on the safe side, the next fish are getting bottled water from out of the hamilton region.