I've had 2 Dalmatian Mollies for about 3 weeks. I lost 1 within a week and just lost the other. It appeared to be dropsy or swim bladder in each case. I do PWC's faithfully. Water tests are good-0 ammonia, 0 nitrate and 0 nitrite. Ph around 7.2. Could this be diet related? Are they tough for beginners? They were part of a community in 38 gal tank with 2 MM platys, 6 tetras and 2 other community fish and is a planted tank. All other fish are fine.