I think you could speed up your grow and have your day#20 plants looks more like this:
https://bucket.growdiaries.com/static/post/photo/95291/4491886_grow-journal-by-malumprohibitumcustomnorthern-lights_m.jpg
It looks like you were flooding those poor roots with water m8. By adding less water you will allow more air to get into the soil. Imagine a sponge; put it under water and press on it and you see all the air escaping, but if you water it plenty before trying same procedure most of that air will be pushed out, leaving your roots with a lot less space to exchange gasses in. Adding too much water will be like shrinking your container size 10-100 times. If you are having a hard time to resist watering, plant an air stone in the middle of the soil, connected to an air-pump and you will be able to flood it with as much water as you like, the soil will still be aerated๐ Good luck with the grow, looks like you got everything else in order, plants got a healthy green color --๐