White mold coating on clay pebbles

[YumBubblegum]

Sup fellow growers!

Was just checking my ladies and noticed that there was a coating of white mold over some of my clay pebbles.

Now I've got two 12.5 L buckets going.
The other plant has no mold over the pebbles??



Here's how my roots look in that bucket.



Should I be worrying? I've pointed a clip on fan underneath my scrog screen now blowing under and through the plants to help stale air from getting captured in the buckets.