Spots - need help

Ok, so I have a pretty basic closet set up with a single 600w full spec light, Temps are usually 70-80 but exact humidity unknown.
Soil is FoxFarm Strawberry Fields which I read that people have had problems with also.
Plants are still vegging at 9 weeks old.
I have General Organics BioThrive grow for nutrients (4-3-3) and gave the plants a half strength dose about every third watering in weeks 4 to 6.
Originally had some curling under/clawing and chlorosis. Thought it might be Nitrogen tox at first so after I transplanted to bigger containers I cut the liquid nutes out and just watered them with pure distilled water (pH 6.3-6.8) for weeks 7-9 on about every third day. They started doing better after the transplant and then started to see some interveinal chlorosis so I gave a half strength dose of calmag twice in the past 2 weeks thinking it could be mg deficiency.

Now I’m starting to see some more curling, brown spots, and reddish/purple stems.

Any suggestions of what I need to do or stop doing?

Also going to test runoff pH today to see if that may be an issue. I will edit those results.

Edit: pH of my runoff is low, about 5.3. Could that be the issue?

 

I tested the ph of my runoff which was low at 5.3. Could that be an issue?

 

Could it be the strawberry fields soil? First time I’ve used it, says it’s low nitrogen high phos and potassium