My first issue in my first growth :-(

First - don't panic. Second, these are autoflowers and don't like nutes for at least the first couple of weeks and when you introduce nutes, you should do it gradually - like 1/4 or 1/2 strength - so I would tell you to cut back on the alga grow... the root stuff is fine. Autoflowers are also extremely sensitive to stress - and transplanting them is stressful so unless you do it VERY gently, without disturbing the roots at all, the plant will go into shock which I think is what is happening here. They DO look to be fairly strong and I think they'll recover in time for them to go into pre-flower/flower in the next couple of weeks. Don't worry about the yellowing leaves - they are just "beginner" leaves and whatever happens to them will be ok. For now, just make sure they're being watered without being constantly wet... let them dry out between waterings/feedings and DO cut back on the alga grow by about 2/3 for at least this week... you can increase it next week as the plant becomes conditioned to it. I hope they are now in their "forever pots" and that you are not planning to transplant again... Your idea of doing one of them as a bonsai is probably not going to work - these are not "normal" plants... the stress you will cause by trimming leaves and roots as in a regular bonsai operation will only ensure they do nothing as far as giving you a harvest and will die off in a MAXIMUM of a month or two without producing even one bud... These are NOT plants that will live for years and years unless you have a photoperiod and keep cloning it and treating it properly. Good luck! I hope they recover in time for flowering! They SHOULD!