Stick your hand between the bulbs and the plant. If you can keep it there without getting too warm, temps are likely ok. You have a fan and fresh air on 'em?

Too much nutes, and wayyyyyoverwatering. Miracle Grow All Purpose has dosages listed for a two week period. (at least they used to when I was still using it) What is the specific MG nutrient you mention, and it's N-P-K, and it's listed schedule?

Cannabis grows best on a wet/dry cycle. If not letting the soil dry-out, you risk a myriad of problems. I'd wait till soil is dried-out a tad and carefully slip the rootball out of the container to check root growth. Should be nothing but healthy white roots.

Mixing products from different companies is not recommended. Different companies put different levels of each nutrients, micronutrients and heavy metals into their formula's. Very easy to overdose without going past the N-P-K limits. N-P-K could still be in range, but combining the different company's nutes can double or tripple-up on the micros and metals...Pick a winner and stick with it. :thumbsup: I recommend the easy to master Fox Farms trio pack. No company affiliation, I've just been using the stuff for quite a few years.

With my 3 gallon plants, I feed 'em 2 times a week. Monday and Thursday.
I mix the nutes half-strength, and give my 3 gallon flowering ladies about a quart of that solution each feeding. During the winter, if I do need to water inbetween, I'll add a quart of clean, properly ph'd water to last to next feeding day. During the summer months I often have to water daily. (I live in the desert)