both plants need help

I’m growing two plants indoors (4th week of veg) that I got from seeds from a bag. I wasn’t hoping for much but everything was going better than I thought it would until recently. Each plant has a separate problem.

1) Plant #1 was getting big so I decided to repot it. Unfortunately I carelessly took it out of its pot and cut many of the smaller roots off. Checked on it a few hours later (now in the new pot) and it had completely wilted, so much so that I was sure it was dead. Now, a day later, the uppermost region is looking pretty decent and there is some new growth coming from where secondary stalks meet the main stalk. Most full leaves are still dead-looking though.

Should I leave it as is? Should I cut off the dead parts and let it regrow? Any other suggestions?

2) Plant #2 is growing at probably half the speed that #1 was. One leaf is twisted and the lower leaves are yellowing. The yellow color is moving up from bottom to top. I fertilized both plants once with 20-20-20 miracle grow mixed with water. Didn’t do anything. Magnesium deficiency? If so, how do I add magnesium? Other possibilities? I find this strange because both plants are in almost identical conditions.

Thanks so much for your help. Hopefully I will sort this first grow out and at least get to flowering if not harvest. Then I’ll know what to do for the second grow!

Q 1 - Yes cut off the dead looking material and let the plant go if it looks like it can hold it self the leaves are nice green colors then ur fine. The plant was most likely in shock and thats the turn of the result.

Q 2 - No its prolly not a mag diff. What nutrients u using is ur water filtered or is it tap water ?

1) It's coming back to life! Dead leaves are removed and its starting to stretch back towards the light. Maybe everything will be OK. Thanks!

2) I use tap water but I let it sit for a few days before watering because I heard some potentially harmful minerals like fluoride will evaporate. The PH of the water (according to the test strips) is normal. Once I realized that there was a leaf yellowing problem, I fed the plants with some miracle grow 20-20-20 solution. I thought it was a mag deficiency only because I assumed it couldn't be an N deficiency since I had fertilized it with N. What are some possible reasons that the fertilizer didn't work? Should I try again and then flush if it doesn't work? Other suggestions? Thanks!

yes tap water left out for a few days works well, if you dont let it sit all your tips on your plants turn brown from chlorine burn

I used to let my water sit for 24 hours so the chlorine could evaporate, but not anymore. If you let it sit, the oxygen dissipates along with the chlorine. There isn't enough chlorine in the water to harm the plants or outweigh the benefits from the oxygen. Since I've stopped letting my water sit my plants have done much better.

Thanks to Babygro for this piece of information.