In picture number six it looks like the sunlight is hiting your tank, can it be? When this happens in any of my tanks (just a few days during the year due to the sun position seasonal changes, even very early in the morning) I have always problems.
Diatoms in my tanks have always been related to non vacuumed dirt at the substrate level, most of the times on inaccessible areas under rocks or wood. Amazing when you dismantle the tank and you notice the amount of debris your tank has and the substrate can store in the first centimeter. Mulm and 'dirt' can certainly work in some tanks but not in my C enriched tanks, my guess is that you need low light-speed, good oxygen levels, low soil disturbance and lots of biomass.
Jordi