What this might be? Plants are 4 maybe 5 weeks into flowering, grown in compost and fed comfrey mixed with a small amount of tomato feed, 2 are suffering fromn the same problem. They get taken outside in the morning and back in at night. Looks fungal to me but being an amateur to all this i dont want to self diagnose the wrong thing.
I just had a spider mite issue and that looks alot like it. Id look under the leaves real well (with magnifying glass if you have it) and look for little white eggs along the bottom ridges of the leaves, and tiny spiders crawling around.
Yeah dude that looks like mites. Get the neem oil and spray your plants down at night. Then get yourself some Kelp and spray your plants down the next morning. This will open up the pores that are clogged with neem oil in them. Do this every 4 days because that is the length of time it takes for spider mite eggs to hatch and lay new ones. Do this for about a month consistently and you should be mite free. Good luck bud.