Dears, UPDATE:
So by the time I have posted here initially, I have flushed my three plants with 6 PH water, and after some advice regarding too much light here, I decreased the lights from 60k Lux to around 25-30k now. I've also added lots of perlite to the new seedling's new transplant pot. A day after I decreased the light (which could or not be related), I noticed that stems were getting longer/taller than their usual stunted rate. I was not sure and thought maybe I am fooling myself. Today I can CONFIRM that the two big plants are getting better! Growth rate is indeed much higher, and the branches are getting longer and moving further away from one another (compared to before where there was no changes in length but A LOT of foliage). What made me confirm is that one of the plants that had very curved leaves from the sides now began going back to being broad and wide like it was before I transplanted them into the new soil. I think we are getting somewhere! Thank you!
Could this all might have been from the excess light? Or does flushing usually work like that?