Everything seems to be going wrong with my aquarium at the moment. One female guppy died last night with some sort of fungus and a platy seems to have got it. Another guppy is just laying in the plants not moving at all. All of the fish are staying around the surface of the water. Ammonia levels are 0 but nitrites are high, very high. So i did a 50% water change, and if anything it has made things worse. I am treating the tank with eSHa 2000 and am on the 3rd day of the does. I don't know what to do?