Growing in coco, does this set up work?

Hey guys! Long time smoker first time grower, Mr. growit has been a staple in my learning experience and community pride. Great content and the knowledge base is just amazing. So here's my thing

I'm growing two Charlotte's diesel and two triple scoop in 60% coco 20% castings and 20% perlite. I'm just hitting 3rd week of seedlings growth, been using distilled water and keeping moist, they are in potting cups sitting inside of 7 gallon fabric pots. Grow lights are two 1200w led tolys full spectrum hanging about 20 inches above seedlings at a ppfd of 500 ish in a 40x40x80 tent, carbon filter and two fans.(pictures to follow) I've started feeding a 1/4 dose of hydroponic plant food and ph to 5.8 with auto watering system that waters for 6 seconds every 16 hours along side of spritzing distilled water every second day. Also running a heating pad to keep soil warm at 78° and rh at 60% as best I can. Now finally here's my question, seedlings are growing very slow and pale, I'd like to know if this is normal growth and can anyone see if I'm doing anything wrong? I do plan on starting calmag soon but feel like it might be too early. Any advice or direction is greatly appreciated.