What ppm?

I have had these ladys growing for almost 3 months now and they have seemed to have stopped growing? What could be the cause of this? Ph is 6.2 temps are 71 for high temp and like 60 low. Giving nutrients every other watering. Feeding around 600ppm could they use more? Back utopia haze, middle tangerine dream, front money bush.

What medium are you growing in. Nutes using? Lights? Humidity?Temps could go up some.

Ffof. General organics nutes, 8bar t5 4" and two vertical led, hum 32%