fungul infection?

[kay_w]

I have recently had quite a few fish die in my tank, at 1st i didnt know why as all my water tests were fine, then the other morning a saw a cory covered in a white opaque coating, it didnt look "cotton wool" like or fluffy, so i treated my tank for slime/velvet.. however i have some plants in the tank and they do now have cotton wool like bits on them, but i dont know if this could be debris from the tank as i took out all the slate so that the treatment could circulate better and some of the dead fish i found behind the slate at the back were also covered in cotton wool like stuff, also when my guppies were dying their tails were eaten away as tho it was fin rot.
so does this sound as tho i should have gone for the fungal treatment rather than the slime 1, and if so is there anything i can do now?