Lol. Man oh man bro, those poor little babies
you didn't pour pure h2o2 on the hydroton did you? Or dunk the plant roots in pure h2o2 did you? That'll stunt them A LOT! The root color could just be discoloration from the hydroton if it wasn't 100% rinsed, but it could be from a number of things as well. You shouldn't need calmag yet, are you using tap water? You're doing way too many things bro, it'll be really confusing if you fix a problem to know exactly what you did that fixed it. Here's my suggestion, I bet if you follow it for 2 weeks, the plants will survive. Transplant them into the 1 gallon pots. Make the water level just touching the plug. Flood every 6 hrs. Use 500ppm nutes. No calmag. PH 5.6-6.1. Leave them alone! If the plug is drying out, Raise the level a bit more, but don't flood the entire plug. I say flood the bottom 1/4 and hand water 1x a day, that should be plenty. Then leave them alone and don't move them at all for 2 weeks. You don't need 400w yet, that'll just cost you money and hurt the plants at this stage, use floros bulbs. I guarantee if you do this, in two weeks, if the plugs don't dry out, they'll be 5" taller and on path to becoming healthy. It's going to take a long time to recover after reading all you've done to the poor little buggers, I'm not trying to sound mean, so don't take it the wrong way
you'll get the hang of it, you're just giving them way too much love bro, I can guarantee if you didn't pour h2o2 on them, take them out of the pot and the root plug stayed moist, they'd be 12" tall within 30 days from popping the seed