You have to give a bit more info if you want anyone to be able to tell you for sure what is wrong.
Temp, light, how old they are, nutrients, ph of medium etc.
If not a quick look around the forum should give you a few clues![]()
Ok will thanks again guysLike Warble said, i think it may be old lower leaves dying of. If you see the yellowing starting to affect new growth you probably have a N deficiency.
Watch it for the next 2-3 days, and see if the yellowing are contained to those leaves. If you see the yellowing spreading, flush your buckets, and give them a new batch of nutes![]()