Does anybody know what this is?

[Stanman]

This is the first time I've ever experienced this in the several years that I have been Reef keeping. Does anybody know what this white fuzzy crud is growing on the underside of my rocks? It's clear and looks like peach fuzz. When I was doing a water change I tried sucking it off the rock with a brush attachment but it seems to be sticking to it .

 

[Tahoe61]

Are you dosing any bacteria products?