Help!!!!! yellow spots on leaves.

Hey guys, I need help. 1st time grower. I have 5 autoflowers going on 18 days. They all have started to get yellow spots on the leaves. 400w mh, vented closet, techniafloria starter nutes, roots 707 soil, finger test for watering. Had to use diatomatious earth to get rid of gnats. But now this happened. Please let me know what you think.

I sprayed with fox farm "don't bug me" spray as soon as my lights went off one time to kill gnats. They had 6hours with the lights off after spray. I haven't seen any bugs since the treatment even on the under side of the leaves. The leaves also seem to be kinda sagging a little. Any ideas to check out don't hurt...thanks for any suggestions/help you can offer.