When I began having trouble with mould forming in my glue pot,
I discovered it was due to my covering the pot when not in use.
Removing the cover eliminated the problem, but then exposed the
glue to evaporation which I understand is bad for the glue.

I now mix up small batches of glue in baby food jars, put on the
cover, and store them in the refrigerator.  To use them, I zap one
in the microwave a few seconds (not long enough to boil) and put it
in the glue pot.  Never have any more problem with mould.

Bill Maxim