Need help identifying plant issues

Copied from roll it up; I haven't gotten much help!

Light: QB 240W LM301H + Epistar 660NM @ 26" from canopy - Dimmer set to 70%

Tent : 2.3' x 2.3' x 5.3'

Ventilation: 2x 6" fans - below and above canopy

Exhaust: Hyperfan V2 6" + Carbon Air Filter

Intake: Passive

Temp/Humidity: Day 25-27c @ 50-55% RH / Night 18-20c @ 50-55% RH

Medium: Promix BX + 60-80% perlite + Dolomite lime (1tbsp / gal)

Water: Tap - 150PPM @ 19c - left out for 24hours

Containers: 3x 2gal - 1x 3gal

Stage of growth: 6 weeks, veg, 6" tall

Strain: Wedding Cake - Feminized

Nutrients: Botanicare Pure Blend Pro Grow (9ml/gal) + Liquid Karma(3ml/gal) + Cal-mag plus (3ml/gal)

Feeding: 950PPM every water until 10-15% runoff @ 6.3-6.4 pH - every 3-5 days

Runoff PPM & PH: I haven't measured runoff PPM or pH in a few weeks. Last check the runoff pH was @ 6.4

Pests: Fungal gnats treated with yellow sticky traps

Symptoms: Yellowing of leaves starting halfway up the plant and browning rust spots. Lower leaves are unaffected.

Suspected issues: pH fluctuations, cal-mag deficiency, light intensity

These girls are just over 6 weeks old. They were stunted early on as a result of improper watering/feeding, too much perlite (causing the roots to grow only near the bottom of the pot), and reusing soil that was void of any nutrients (I baked it in the sun before reusing).

In the last 3 weeks they have been growing at a healthy rate. However, last feed I started to give them cal mag after noticing some rusty colored spots.

3 plants are in 2gal pots, 1 was recently transplanted to a 3 gal. I plan on transplanting the 3 plants to 3gal pots before next watering.

Any help is appreciated,

Thank you