can someone tell me what MIGHT be causing this

Many things might be causing it.

Sounds like it could be spider mites if the dots are very small. Look on the under side of the leaf with a magnifying glass to check for them. Outdoor grows get mites too, especially in your climate.

Could also be other bug damage.

Could also be fert burn or deficiency.

Could also be mold spots, but not likely with your temps. Do you keep them too damp?