Dude, use lime. Toss a little in your watering can, fill with water....put enough so that the water's opaque. Don't throw a whole handful in there, but you don't have to be scared about using it. It's just chalk. Get the pulverized lime. You can get a 40# bag of it at Lowes for like $4. Should last you forever. It'll bring the PH up and supplement calcium. Been using it in my garden for years, and did the same early on in my current grow. I actually add a little to my soil when I'm mixing it before planting/transplanting as well. I can't say for sure that pH is your problem, but if you want to raise it easily and safely, I highly recommend lime.