Originally Posted by aquandrew
do you have a powerhead pointed up for enough surface agitation? this can be a big problem to your Dissolved Oxygen levels
Personally I have plenty and it still forms, 2 power heads pointed at the surface and 1 power head 2" below the surface. So it is possible that the op does but I can't speak for them. I can say without surface agitation it would be far worse.
The op said they have agitation and it is forming where it is calm, how much flow do you have and how large is your tank?