I have a tank in my classroom(I'm a teacher) and I'm struggling with dropsy. THe fish are dying like crazy. I've done water changes to try and help the problem, but doesn't seem to be helping.
It's an 80 litre tank with a EHEIM box filter and about 3-4cm thick black gravel. The fish are guppies and platies. Temperature around 25 degrees.
I've been using tap water to top up, and conditioned water to do major water changes. Could it be the tap water causing the dropsy? What else should I look at?