Brown spots and leaves tacoing

Thanks in advance everyone!
I've noticed some brown spots showing up on some lower leaves of my plants, one moreso than the other, but nevertheless, still present. In addition, I also noticed some of the larger fan leaves have tacoed up, albeit only on one of the plants. My first instinct is cal/mag but not sure.

Grown in FF Happy frog [5gal pots], popped out of the soil January 1st, no nutes yet, watering with PHed water only till 10% runoff when soil is completely dry [about every 3 days] [approx. 6.5 - I only have the drops/color chart to go by] and grown under a mix of blurple [viparsectra] and white LED [mars hydro] with approx 300w from the wall at 18" above canopy in a 3x3x7 tent.
[2 closeup pics are of the same plant]
Please help diagnose!

I say raise your light because 300w is a lot for young plants. I would raise it to 36in and let the plant grow into it. The stems are red and the leaves are burning up from too much light. Raise the lights to 91.44cm or 36in and keep doing what you’re doing. After they bounce back in a week or two lower the light 6in Your lights may need to be hung at different heights.

Thanks, I'll give that a try.