I did a DSM as well and just flooded a few days ago. The day after I was growing a good mass of mold, perhaps algae ( brown /white ). In hind sight I was using a large amount of fertilizer, liquid mixed with water, sprayed directly on the substrate. It makes sense that once flooded that extra and I mean extra fertilizer was being devoured by something.
I've jumped into the deep end. ( 1st planted tank flooded 4-15-18 ) - Dirted with sand cap - Very messy when water was added.
75 Gal, Fresh Fluval Plant 48" Bluetooth. Co2