The humidity is obviously too high. Lowering the humidity will kill the mold. Hot and humid is what it wants.

It’s a big problem out west where clones are shared and sold at scale. It’s all anyone talked about for years. This is why we tell new growers to source their own genetics from reputable seed breeders. Buying other peoples problems is a known thing.

As a grower, you have to be prepared to kill shit.

I don’t like restricting seedling roots. I’d transplant it soon. Roots are supposed to grow out of the starter media. Clones are different and need a humidity dome unlike seedlings. After you see the few initial roots popping out, you have a few days to acclimate clones out of a humidity dome while the roots continue to develop enough to transplant.

HPS can be cheap to buy up front but buying $100’s of dollars worth of bulbs every few months get’s old. An oil-filled radiant heater is a good option as they don’t produce light for cold nights.