Seedlings usually have enough stored energy in the seed to until the cotyledons open. After that, very light feedings using either an eye dropper or a light mister, as they have neither the leaf structure nor the roots to support big meals. If you don't already have one, get a EC/PPM/TDS meter and mix a TINY amount of grow nutes + a TINY amount of Kelp totaling < 100 ppm until you get to the 4th node, then double to 200 ppm to a max of 4-600 ppm just before switching to bloom hours and nutrients. I have had many plants show sex at 300 ppm in hydroponics
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