Brown tip seedlings leafs

My 4 girls are growing well, then this morning I noticed one of them has brown on the tips of it leafs. All 4 girls are in the same environment and set up exactly the same and have received the exact same nutrients and are the same strain. The others don’t have brown tips. Any ideals or suggestions? They are in rapid rooters and set up so the bubbles barely hit the bottom of the rapid rooters, they aren’t soaked but are pretty wet. Yet all 4 Have the same amount of moisture in them. The grow tent is 78 to 81, good air flow. The humidity is a little low, mid 40’s, I cant get the humidity any higher, I tried an humidifier and Containers with water containers with water in it in them (tried the containers with and without a small towel)

Seedlings can't handle nutes early on some might be able to handle more than others since not all seeds are the same, even if it is the same strain you should rather start feeding nutes after the cotyledons fall off, this is a sign that the roots are well established and that your plant isn't in seedling phase anymore and that it is in vegetative phase, once your plant reaches this phase it is ready for nutes and will start growing like a weed

Thank you

No problem