don't know if I can be of much help, I use aeroponic, but I notice in my setup that if the PH was off just a little bit it made a big difference. Maybe if you PH your water first that might bring some good luck. I also use Fox Farms but am currently using Grow Big and Tiger Bloom. If your in flowering stage then I do remember hearing that the fan leaves will yellow a bit in preparation of producing flowers. I may be retarded though im on my first grow still. And i just started flowering last friday. Good ,luck man