It's hard to say what's wrong when you use a soil mix which contains slow release fertilizer. Do you have a means of checking the PH. Upturned leaves can be caused by high PH.

Herbus
Herbus Reviewed by Herbus on . What's the real deal with yellow leaves? After doing some searches on here I haven't been able to distinguish what can cause yellow leaves. I've read it could be not enough N, too much water, not enough water, too much fertilizer, etc... 2 out of 3 of my plants have some yellow leaves at the bottom, they are about 4 weeks old. I'm using soil that has fert built in, but my one plant is perfectly green so I doubt it's burn from the ferts. The biggest plant has a few small yellow leaves at the bottom that are completely yellow. Rating: 5