In my garden, in the winter, the soil retains water longer than during the summer. Tiz why I add perlite when cold/humid. If the lower root zone isn't being allowed to "air-out' a tad, you can develop problems with oversaturation. There is usually no need to completely saturate the soil, except during a flush. You mentioned half-gallon of water per 3 gallon (or so) pot, I believe, plus additional waterings of around 1/2 gallon. In my garden I go through about half that. Did you by chance add perlite to the potting soil before use? If so, perhaps you use more perlite than I do which would retain less moisture when watering.

Did you find-out the MG schedule for their nutrients? (is it a weekly schedule that's listed, or does it say to feed every other week?) I'd find-out for certain, and start following the instructions.

Exactly what are you using to determine ingoing/runoff ph?

How long have the been inside the pots they are in? Just curious, because it doesn't usually take long to fill-in the rootball. There shouldn't really be "plenty of room" in the pot. Should look fairly tightly-packed unless it's only been a week or so.

Even if you cut the dosages in half for the Scotts or the MG, they are still about twice as 'strong' as other 'cannabis' nutrients. Compare their numbers to 'standard' cannabis nutes.

Are you using superthrive or something similar?

Is there a fan on 'em, for proper ventilation of heat and providing fresh air?