White Slime

[subman]

I don't think it's sponges but with out a better picture I can't be sure. I had a very similar slime before and lost everything except the hardiest leathers and polyps. In my case it was from running bio pellets. I started out with you much and the bacteria exploded in population and the high population of bacteria used most of the available oxygen.
I would do a good sized water change, and start that skimmer and don't add any more additives.