i have the same prob by the sounds of it i have been tryin to correct it for 4 weeks now and still no luck.my plants are almost 3 months old and in the second week of bud.kept pushing 12/12 back to try to regulate it.now after 3 weeks of trying to keep my ph balanced i am still noticeing that my run off ph is 5.8 after 3 weeks of putting 6.5 so now i have up it to 7.0 ph in the water hopefully it will balance.my nutes have been put in the water at 500ppm-600ppm and the run off is 1100 this is the first time i have been so fucked up i don't know where to turn.i have been posting pics and questions and not really any help you get some people who say left and others who say right...up...down any ways keep an eye on ph levels both in the water and the run off same goes with ppm (NUTES).if your soil is already mixed then you should realy check those often.take my word for it