[Pescador]

I just had a similar reaction with new filter socks. I use a set of three 7" socks and just purchased a bunch in bulk. The first set I rinsed in tap water and no problem everything was fine.
The second set I didn't rinse and I got quite a scare. My skimmers started foaming like nothing I've ever seen, thick like soap suds, the foam was standing up a foot high.
I thought my tank was toast. I shut everything down and rinsed them in tap water and started up again, they foamed a bit and then quit. Everything is fine in the tank but I sure got a scare.
What ever it is on the polyfilters foams like crazy but is non-toxic, and rinses out easily.