what strength is your nutes? you should really pick up a tds meter. you can buy one off ebay for $20usd. your plant maybe absorbing a lot of nutes after coming out of lockout due to acidic rezwater. with my nutes i use ro water and i can follow the feed chart from the nutes and not be too far off but if i used my tap water, most of the ppms would be in plain water alone making the rez strong. tds meter would help troubleshoot a lot but right now its somewhat a shot in the dark