Edges of Leaves curling upwards, Can't figure out the issue, thank you for any advice!

Aloha, these seedlings sprouted about 3 weeks ago, everything seemed to be going smooth and they are still growing but I have noticed a strong upward curl taking place on two of the seedlings, a 3rd is lightly showing. I have more than adequate air going in each bucket, light seems mild but maybe it's stronger than I think? It's a Spider Farmer Dimmable SF-1000 LED and there is a nice mellow air movement. PH is good and I'm keeping the PPM around 450. Any advice or tips to remedy this would be super appreciated.
Mahalo~
 

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