That does resemble sulphur deficiency, but I'm not entirely sure about that. Find an all-around fertilizer, one that has boron, sulphur, mg, mn, etc., and give that plant a dose as stated on the container's directions. Giving magnesium won't help with a sulphur def. You've got to give sulphur if that's what's missing. Many hydroponic ferts will have everything a plant needs. Supernatural comes to mind. Ask for this kind of thing at your grow shop.
polishpollack Reviewed by polishpollack on . yellowing leaves hi, i've got 5 plants that are in there second week of flowering, all are doing fine but one, about 3 weeks ago the leaves at the top started to lighten and yellow, its now yellow about a third of the way down and the buds are tiny,:( i repotted about 4 days ago and it did look a bit rootbound, i have noticed a couple of little black flies in the room as well! anybody help!! Rating: 5