Interveinal Chlorosis. - I jus checked the FAQ's section and It looks as if its 1 of 2 things. Ill start with Ozone, it also says Magnesium., but if you are not using an ozone generator than that's not the issue. Start with the Epson Salt, CalMag, or MagiCal

Check this out: Text (Ozone Damage - Figure 8)
killfrenzi Reviewed by killfrenzi on . Can't get these brown spots to stop... maybe its not a nute issue? Heres a few pics of a plant leaf from a female I have in flower right now. Seems to be happening to some degree on most of my plants, brown spots forming around the veins on the leaves. Its been progressing very slow and steady, so I've tried everything I can think of. At first I thought it was a mg deficiency, so I fixed that, then phosphorus, wasn't that either... soil ph totally balanced, and flushed and then fed again to reset the nutrient amounts in the soil to be sure. Starting to wonder Rating: 5