After checking for rootbound, I'd cut way back on the MG ferts. 1/2 tsp per gallon per week is what I use. (When I run out of my cannabis nutes, and MG is all I've got. Primarily for houseplants, but...) Dosage listed on the MG All Purpose is for two weeks per instructions.

I live near Vegas, and our wellwater comes out at 7.9. I use 1/4 tsp of General Hydroponics PHDown (phosphoric acid) per gallon of water. If you really live in/near Vegas, I'd recommend you hit Star Nursery and grab some Dr. Q's Filthy Rich Potting Soil. I've been using it for years. (add perlite during winter to lighten the soil)

If using a color-coded test, (strips or freshwater aquarium kit) the runoff ph might not be as high as indicated. Are you using a ph pen by chance?

If you are getting serious about growing cannabis, you'll likely want to check on a source for some 2 or 3 part nutrient packages. More flexibility and proven results. Personally, I stick with the Fox Farms trio.

Have you made plans for dealing with heat issues when it warms-up...? Might be some helpful tips for ya in my signature.