I have not tested for silicates. I need to get a test. I just assumed it to be silicates since the crap looks a lot like diatoms to me. Nitrates and phosphates are zero, and very well could be, since I am growing a large mass of chaeto and running clearmax while having zero other algae occurances.
If it wasnt for that dusty junk and the scratches all over the acrylic, my tank would look flawless.
Since you have the stuff too, and your tank IS flawless, any idea what is feeding it? Could it be lighting periods as well? I cut back my light by 2 hours (8hours now) and am going for a blue tank. Doesnt algae like the yellow end of the spectrum rather than blue?