How old was the used AS? I'll bet it was adding the AS that is causing a slight melt to your crypts. With your automated dosing seems unlikely to be a nutrient deficiency.
The AS can alter your conditions enough to cause crypts to melt. I've done it on a smaller scale in a 10 gallon tank. Wiped out a nice little grove of C. keei 'jambusan' and C. cordata 'zonata' by adding some new AS to an established tank. It wasn't much AS but enough to change the water conditions to cause the melt.
Strange that the bullosa seem unaffected. I would think they'd be affected too.