The diatoms are on the sand bed. I took those Pictures right after a water change where I stirred the sand a bit. I thought it may be a nutrient issue as well but tested everything and it's all good. Po4= .01 no3= 5. I keep polyps just about everywhere in the tank. I think most people don't give them (certain ones) enough light. Most can handle and actually like a good amount of light.If it's diatom on the glass could it be PO4 issue? And the acro browning might be nutrient related as well. Nice setup. The polyps looking great. I notice you have them higher up in the tank instead of on the bottom.