Look into the cyano-bacteria. Sounds very much like what happen to me.

Only way to take care of it for us was Physan20.

Nothing will touch it and it starts a bio-slime that stay on all surfaces if not cleaned with something that can kill it. It's a kind of clear snot growth and it does not need light to grow. In most cases the good bacteria keep it in check but when conditions are right in hydro non of the main products will help. They are dealing with algea type problems and that won't work here.

You got alot of reading to do now . Hurry no time to waste you might be able to save them little ones.