When using the aquarium kit to test ph, you can't use it for accurately testing run-off. The tinting of the water skews the color-coded results. Clear water only.
Pro Mix is a stable medium and doubtful the ph is crashing already. Which Pro Mix formula are you using? Would raise your water's ph to 6.7ish on watering days, perhaps 6.9 on feeding days. (test before before adding nutrients)

Looks like ph is too low, light is too high, and watering should be deep enough to add moisture to the lower root zones. Heat and fans require more waterings, or more water added per watering. Be sure to get the water to the lower root zones with every watering, but don't keep the roots soggy.

Personally, I'm not a big fan of a 24/0 schedule, and I have had the best results using 18/6.

Find the AN nutrient schedule online, and starting today...stick to it. :thumbsup:
Rusty Trichome Reviewed by Rusty Trichome on . 3rd time is a charm I have 3 kids currently all with something going on with it. I will fill out the trouble shooting form and post various pics. Any input would be AMAZING. Thank you. What is your experience level? Novice Your Equipment: .1) Type and wattage of lights. 1 600w Super HPS .2) Distance from tops? 2 ft .3) Reflector type? Vented Hood (hydrofarm growzilla dual bulb) .4) Is there a consistent fresh air supply? Yes .5) Do you have an exhaust fan and a circulation fan? No-Exhaust Yes-Circ Rating: 5