Over/underwatering?

I'm starting some seedlings in a little cardboard box w/ 3 42w CFLs in some regular potting soil, everything's been going well until i noticed a little yellowing on the tips of my biggest plant. I water them about once a day, soil is usually moist but not too wet. Cups have drain holes in them, the box has a constant airflow, and the temp is around 76-78 degrees with a peak of 80 degrees. Humidity is around 40%. The plants are about 2-3 inches away from light source.

over watered, what kind of soil?

Don't water once a day. Let the soil dry out. In that small pot you prob only need to
water like 1-2x a week.
Are you feeding it too cause it looks like nute burn too

looks like my mini grow operation in my closet, i have the same thing on my plants. Me thinks it's nute burn cuz a few of my babies are in Miracle Grow and they have those stupid nutrient balls that feed the plant every time you water :/

i think i may have been over watering mine for like a week then could this do any damage to it??

thanks, i'll cut down on the watering

the burn visible on the bottom picture is from a little nutrient ball that popped between my fingers and got on the leaf, haven't given them anything other than water. Out of the 7 seedlings growing, this one is the biggest, but the only one with yellowing or curling leaves.

i'm planning to upgrade to a 600w setup, just gathering funds in the meantime, going to use this as a clonebox later on

thats is for sure over water if u see yellow ttry a low nitrogen seedling nute to keep them going strong