^^ I think Rusty has it right as usual :greenthumb:

But for next time - Have you thought about 5 gals instead of just the 3gals? You can get away with the 3 gals with clones, but the root systems of plants from seed are much larger and also like to have more room to stretch out.

I've also noticed that transplanting a week or two into flowering to a new pot helps with the problem of ph drop/buffer depletion.
bigtopsfinn Reviewed by bigtopsfinn on . need help on yellow leaves and brown spots down center What is your experience level? (first timer Your Equipment: .1) Type and wattage of lights. 600w hps .2) Distance from tops? 8" .3) Reflector type? enclosed air cooled .4) Is there a consistent fresh air supply? yes .5) Do you have an exhaust fan and a circulation fan? exhaust yes circulation no .6) What are the bulb wattages, kelvin ratings, and schedule? 600w 12/12 Rating: 5