my guess would be to flush. it never hurts to flush every 3 weeks or so anyway. Then add something like Cal/Mag to the diet...looks like a cal mg def. to me, or it could even be some sort of pH problem but a good flush and some feed with cal mag would probably do the job. I believe you can use epsom salts if you can't get Cal Mag, check the forums for amount of epsom salt.

Ok another thing is what kind of soil? Does it have feed in it already? It could also be nute burn, we need more info.