That pic really does suck but you just perfectly described the chewing marks left by flying pests (whiteflies and/or thrips).

Dust a little diatomaceous earth around, and give them a squirt of neem.

Keep neeming them and you should see improvement.

Go to Home Depot and buy yellow sticky traps.

Post them right at the base of the plant. If you still have any pests, they will land on the traps and you will be able to see them.