That actually looks like light bleaching to me. I have the same thing on a couple of my leaves from when I got them too close to the HPS. What kind of lights are you running and how far are your plants?anyone?????
don't think it's calcium (from rui plant problems and cures stickie) : Calcium Deficiency:I've just looked on another thread and it looks like calcium deficiency which the plant doesn't take up cal if its cold which my lights off temps can get cold. so it could be that. epsom salts cures it????
Sorry brother, i shouldve clicked this earlier.. drum roll plzz!! u have mag lockout!! prob due to low pH!! trust me trust me brudda.. now its lacking mag BUT not bcos it aint there but cos its locked out.. up that pH my nizzle..well i ve got epsom salts in my soil.. i ll try a tbs in a liter of water just in case this works i ll let u know.
i bet my mother on it.. no worries.Ok cheers mate, my ph is 5.5/5.7 so it could go a bit higher. i'll knock it up a notch to about 6.0/6.2.