Help - black spots on leaves

My plants were just doing fine, recovering from a nitrogen deficiency when I noticed these black spots. In addition, the leaf tips are also turning yellow. First it was only on the lanky one and now its on the healthy one. I was wondering if you guys knew what this was. I did research, and I think its either a magnesium deficiency or bugs but i cannot tell. Any help would be appreciated thanks!!.

Light: 150 watt hps : about a foot away

It looks like calcium to me.

Rusty spots can usually be either a P deficiency or a Calcium and my cash is on Cal.

It's not so simple, you likely have a ph problem in your soil. Feeding it more won't change this. You need to correct your ph, IMHO.

Yeah I would also say a ph issue and it's causing you to have cal or mag problems I'll take a wild guess and bet your ph is below 6.4 if it is it's harder to absorb cal and mag bring it up a bit.