yellowih color

At 30% that light is giving them very little. If it's a 100 W Mars Hydro, 30% is roughly 30 W, and in a 2x2 that's around 180 PPFD average. That's seedling light. Past the first couple of weeks they want 600 to 900, and in a 2x2 that's basically the light at 100%. At 20 inches a 100 W light won't burn anything, so I'd turn it back up, maybe 10% every few days, and watch the top leaves. On the yellow: lighter all over rather than spots or crispy tips usually points at hunger, not light. In an amended soil that can mean the mix is running low, or the pH drifting with tap water. Pale older leaves first is the classic nitrogen look. A cheap pH pen or drops would tell you a lot. And water by the pot's weight, not every 3 days. Lift it right after watering, then water again once it has lost about half the weight that watering added.

Hi ich lass meine 200 Watt immer auf 100% laufen und sie sind noch nie gelb oder haben sonstige Probleme gehabt. Hänge die Lampe auf 60 cm und das war’s. Hoffe das hilft dir etwas weiter aber da hat jeder so seine eigene Erfahrung gemacht. Schaue nach anderen Grower mit derselben LED. Viel Erfolg 🍀.

Lower the light alot 20inch@ 100w?