Spots on leaves: need help thanks

[Doakkelley]

I have some autoflower that have these yellowish spots on the leaves was wondering if anyone new what was wrong thanks.

 

[Bud]

I beleave this is caused by PH fluctuations imo

 

[Doakkelley]

Do you know long it will stick with the plants. And how to fix it.i keep my p.h about 6.3 using organic dry amendments for my nutrients in hpcc for my soil All my other plants in both tents are not having any issues and are growing great. But there is like three or four that show signs of this. Thanks