dimming hlg light and cooking living soil

my buddy gave me a hlg qb120 (heard they are awesome) for free and he said it can be dimmed down to 60watts which is what I need because I have seedlings right now, it has vo adj and io adj which one do I use and what does the other one do?

also i made my own batch of living soil and after 10 days i have some nice fungi growth on top, is this a good sign to have only after 10 days and how much longer should i leave it before i put young plants in?

check your temps over a week and the ph too at the end of the week

make a decision

good luck