If it's brown, "gooey", and has air bubbles trapped in it, then it's probably not diatoms or cyanobacteria; it's likely dinoflagellates. Of course this is based on your description, as I'm having a difficult time making an assessment based on the picture.
Based on the description of your setup in the Tank Specification Forum, I'd say your problems are arising from insufficient water circulation and an inadequate protein skimmer. Removing inorganic phosphates from the water column with a phosphate sponge isn't going to cut the mustard because most of the nutrients in your tank are bound to various substrates (including animal and plant tissue).
Assuming that this is a dinoflagellate outbreak here's what you need to do:
<ul type="square">[*]Get a better protein skimmer.[*]Increase water circulation.[*]Temporarily reduce the photoperiod.[*]Syphon out the dinoflagellates religiously without blowing them all over the tank.[*]Do frequent water changes.[/list:u:3531e57500]
I've gotta head out right now, but when I get back I'll post a more specific reply.