I have had a tropical fish tank set up for just under 3 month so know very little so far but recently I had to treat tank for white spot which seemed to clear up but the water has started to turn yellow and strange smelling, my fish have started to die again but there are no marks on them to say why they died. lots of small snails seem to have apeared from somewhere and are all over the place, in the filter and even on the filter pads which seem to be getting really dirty after just a couple of days. Some of the plants seem to be dying as well but I have no idea whats going on. The only fish to thrive is the plecostomus catfish which has doubled in size since I put him in. The other fish in the tank are neons, zebra danios, angel fish, mollies and platy's. The mollies platys and angel fish have been dying one by one over the last couple of weeks. Does anyone have any idea whats going on or how to stop it?