Is the whole tub filled with those balls or are they resting on top of water?
If you make your own yogurt or kefir, try using a sous vide to regulate temperature while things ferment. Makes for an easy time.
https://video.nostr.build/181291038d13aa3a9fc8aff0bfe2e897e1dd289b3bb209ef8dd0eb223aabc90e.mp4
Discussion
They sit on top of the water. They work great to keep the heat regulated and keeps steam/condensation down.