ph fluxuations

Well I'm not sure what the problem is with my girls, this started just a couple of days ago and they're getting worse fast, other wise, doing very well. My girlies are 3 - Pure Power Plant from seed. 600W. in a 4'X4'X6' tent 50% humidity, (via an, in tent, cool humidifier.) 75 deg. F. (via...