Are you letting the soil dry out between waterings? If not, you should. Cannabis likes wet/dry cycles. Water so that the pot is evenly saturated with 10% run-off, then wait until the pot feels light again. It's not the amount of water you give it that matters, it's the frequency. Too often or not often enough is when you will have problems.

Hard to give much advice without pics, but you will definitely need more light to flower all those plants. I'd recommend a 250w hps or even better, a 400w hps. You can also just add CFL's or fluoros as you go.

Never used a 70w so not sure about the best distance away from the plants, but with any light you can just hold your hand underneath the light. If it feels uncomfortable for you hand, it's too hot for the plants. (Just remember to alternate hands, otherwise you'll have a funky tan ) Then adjust the height accordingly.

Happy growing :jointsmile: