White stuff at base of stem?

its mycellium spray some 1% h2o2 on it

mold. Mold in soil basically. There is a few things you can do to combat this. But it is mold. Look up different types of mold and you'll quickly come across yours. You can use stuff like Trichoderma Gliocladium Copper And a few different things to prevent mold from happening as there's not much you can do in the way of ven in your substrate so you will need to look for something like a beneficial bacteria that fights mold in soil like Gliocladium and use the others as pre applies to prevent it. Hope you fix it soon. But brush up on dif things you can do a pick a method that you can put together as quick as you can. Good luck bro.