a problem with AK 47

Ive got Ak47 auto which is about 5 weeks old. The bottom leaves started to turn yellow and die, and this symptom has spread to higher parts of my plant(to older leaves). From what I have read before posting this looks like N or Mg defficiency, though I was nourishing my plant with liquid form of a nice commercial vermicompost (thats the english name for it) which contains N P K, and other elements (including Mg). What might be the problem? The temp is around 30 degrees(of celscius), Ive got a HPS 70w, fotoperiod is: 18/6.
Could I have added too much nutrients? It may be the wrong pH as my pHmeter died and I'm acidizing my water according to my memory. I've also frogot to mention that the problems started after feeding it with fertilizer without Nitrogen(aiming at the lowest dose possible as to avoid overfertilizing) but with P and K. I'll try to get a working pH meter(my acidizing technique was working so far -.-), but could it be anything different than pH?

photos:
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Not enough magnesium, supplement with calmag

but you also wanna keep your N a little higher during the first stages of flowering, but your problem is a lack of magnesium... MJ gobbles tons of it during flowering and I have yet to see a line of foods that have enough to keep the plants happy