Just needs more circulation. I suggest covering the tubers completely with soil, and take the top plastic off. If you have them in a closet, they shouldn't dry out too fast.

It is just evidence of fungi breaking down organic matter in the soil - The Ocean Forest soil mix is very rich in OM. Too warm and moist a growing condition will encourage its development but it is harmless on its own to the plants/tubers. But it can be an indication you are keeping the soil too wet and that will lead to rot. Soil mix for starting dahlias should be just barely damp to the touch.

I agree that you need to take off the plastic. And they don't really need to be in the closet unless that's the only space for them. In which case, leave the doors open :-)

Thank you cici and gardengal!

They are in the closet because that is the only cat safe place for them that isn't cold. My cats love all plants and dirt.lol

I uncovered them partially this morning but was in a hurry so when I get home I'll do it completely. I'll also add soil and make sure it's not too wet. I tried to only add a tiny bit of water to them but maybe it was too much.

THANK YOU! (I feel much better now)

When forcing, I water using a spray bottle. That way I can make the soil damp, but not wet.

J Pru, good idea. I have a spray bottle, didn't use it.lol

This morning they look ok, no more mold and look much more dry.