I've had problem after problem with my guppies. I've lost a lot of fish recently... It starts with slowing down, clamping up the fins/tail a bit, fin and tail rot and eventually death. I am keeping my water parameters as close to perfect as possible (However nitrate levels can be in the 40's as I have to use a nitrate filter and only half of the water gets treated). Ammonia and nitrite in all tanks currently are at 0. (It will occasionally go up to the second lowest level... don't have it in front of me but I've been working hard at keeping the water as clean as possible. Fish in the one tank I noticed some white/grey areas covering the backs of some of them. Then came the fin and tail rot (and around the edges it appears "wooly.") Then they would die. The second tank filled with mostly fry starts to pin tail and then die. There are a few adult fish in there now suffering from fin and tail rot (slowly dissinegrating) and I just noticed right now one of them, instead of a front fin, it looks like she has a tiny, perfectly formed Dandelion looking growth in place of her fin). I have treated for ich/parasites and different bacterial diseases, nothing is working they continue to get fin/tail rot, occasional white patches on their bodies and now this cottony growth where the fin should be. Could this be a fungus and I've been treating it all wrong the whole time? I must note that the platies and swordtails that share the tank seem to not be effected by it (though they are starting to look a little more listless). What could this be!? I will try to get a photo if I can of the dandelion growth but it is just that, a perfectly shaped dandelion (the white kind when its ready to blow away)... Thanks in advance.