Plants aren't growing fast?any help is appreciated!

My plants aren't growing at the rate they should grow, The plants in the pictures are already 6 weeks old and are tiny. I don't put nutrients because I don't know how much to put. I have a mix of potassium, nitrogen, and phosphorus, but last time I put some my plant died in one night.

What can I do to get the plant to grow more?
any help is welcomed.

maybe your medium...if its packed too tight...doesnt drain...your roots wont grow...

Soil looks thick. Roots might be suffocating. Yes, roots need oxygen to thrive. Add perlite. Or just get some good potting soil.

Like they said above, too compact for little plants. They are also in pretty big pots. Its better to have seedlings in smaller pots they grow better. And try burying those stems down abit those stems looks skinny and weak.

Make sure your letting tho pots dry out between watering ...
Also get those t8 inches away from the tops.

^yea, Looks like that soil holds moisture pretty well and with the pot size would take weeks to completely dry out under t5s..so I'm gonna say overwater