Some kind of sponge on the glass?

[kgb]

I don't think the pics would help, they're so small, and they're on the back of the glass. They're like... Shaped like a sea squirt, but they look hairy. There are some 'colonies' of them behind my PH and heater, and some directly under the filter. They're sort of a baige color... If someone wants, I'll take some pics if it will help.

[skippy2]

You need to try to get a pic. It could be just about anything.

[Pineapple]

A common one is the pineapple sponge.

[mogurnda]

The most common sponge to crop up is the "q-tip sponge." Does it look like this?
http://www.reefs.org/hhfaq/img/faq_sponge.jpg