Did you ever find out if some one dumped something in your tanks?

No the only thing I found was an empty water bottle with the a small amount of some kind of oil in it.

The only other thing that happened is someone dumped a half a container of beta pellets in one tank. I found the leftover remains of that in the filter and in the protien skimmer. Good thing they work most of the time.

Oil and water when mixed up and airated in your skimmer would have produced a milky looking foam. That's probably what happened.

yes it did. it was a white milky substance in the on top of the sump and in the skimmer it was a milky substance and would not skim. As a matter of fact it wouldn't skim for about two weeks. I had to thoroughly clean my whole system up and scrub my sump down as well as my skimmer.