IMO blow off those areas and wait. Here is a tricky thing to consider also. How many cells were in the sand not getting exposed unless the sand was turned over with every dose. This is a fact to consider.
To me it does not look like heavy cell reproduction. Observation is the best thing you can do right now. Remember each tank is different and the amount dosed in your tank with either be or not be adequate. This is what makes it so hard and tedious when I do these studies. People want dosing amounts NOW and that's where I say "it is not ready".
I thank everyone for sending me such inspiring PM's lately! Trust me guys work continues