Sensi skunk fem

So this week I topped all my sensi seeds also have started introducing cal mag I’m feeding each plant around 500 ml every other day just before lights go out still running 18/6 light system two desk fans blowing air around! Two humidifiers as struggling to keep ph at 50! Not sure if I should buy a oil filled radiator as night time temperature is still around 15 degrees when lights and fans turn off! Not sure if I should be adding more nutrients? Some lst work on plants as some leafs are getting huge! Not sure if I should cut them?