If its trapping bubbles surely its not diatoms? If anyone you know has a microscope look at a sample under that as they are really easy to recognise. Trapping bubbles suggests dinos to me, I've recently had them for a while, they do seem to have receded to me at the moment but who knows! I have heard many give up the hobby because of them :-( I raised my pH to about 8.4 (from about 7.9) with outside air going to the skimmer (ramping skimmer up to full air too). I also started adding a lot more food (like D+D coral paste), which has driven my nitrogen and phosphates up slightly (deliberate). Not sure if either of them helped but if I do think one of them has helped. I cleaned the tank out a few days ago of all the dino slime I could get at and its still spotless (only minor WC), other than a tougher coating on some rocks, which I think is not dinos (Looked at under microscope this is filamentous, but tougher than the cyano I am familiar with, so I'm not sure what it is but I am pretty sure its not the slimy dino stuff which covered it and which looked completely different under the microscope).