Thrips don't cause the entire leaves to turn yellow, do they? I can only speak from personal experience, but my leaves got spots in various places, but no yellowing like that. Perhaps his infestation is further ahead?
Thrips lay eggs on the top of the leafs and feed on the bottom, thus yellowing them out. If you got a good loupe, check out the bottom.. they like to hide along the veins of the bottom of the leaf. You should see some poop too.
Oh!.... and the solution is some Capt. Jacks... (contains Spinosad).. spray the tops and bottoms of leafs right before lights out. Never during lights on. Repeat in one week. Assuming you're in veg still.
Oh no, they are. I just thought, based on the first pictures, that perhaps the primary issue was nutrients and that the little thing was a stray bug or a different issue altogether.
It's based on pyrethrum, natural and not harmful to your plant but very harmful to thrips. It also works against all kinds of other stuff, so it's worth getting IMO.
Or Spinosad as suggested, never used it, but I've heard good things.
Thrips don't cause the entire leaves to turn yellow, do they? I can only speak from personal experience, but my leaves got spots in various places, but no yellowing like that. Perhaps his infestation is further ahead?