It's hard to tell without a pic but you MUST know the pH. You mentioned that they are clones, how old are they? Do they have established roots yet?

It could be nute lockout, the soil could be too hot (nutes), or it could be anything.

If you dont have a pH tester, get some pH strips. They are very cheap and work well enough.

DH
dillhole Reviewed by dillhole on . Leaves On My Plant Are Almost ALL Beginning To turn Yellow I'm AFRAID It's Gonna Die! Well I'm a "FIRST/SECOND Timer" Before now I have only grown small plants from seed and sold them at about one month old... Your Equipment: .1) Type and wattage of lights: OUTDOOR. .2) Distance From Tops: N/A .3) Reflector type? N/A .4) Is there a consistent fresh air supply? YES, definatly Rating: 5