Since setting up the jar aquarium two weeks ago the water level in the jar has been rising. I removed water multiple times to lower it back but it kept overflowing which had me very befuddled last week. I even marked the neck of the bottle with the height of the water at different times of the day. The water does go up when the sun warms the bottle, but it does not return to the starting point the next morning. It slowly continues to rise.
But I think I finally figured out the cause. Can you see it in the image below?
Bubbles. There is a large amount of gas trapped beneath the mud. These bubbles are created during the process that is breaking down the decaying plant life within the muck. The process probably goes faster when the sun hits warms the muck.
In the image above you can also see the tunnels that the worms have been making in the mud. I haven’t been able to capture a good photo of them.
I gave the bottle a good jolt and tons of bubbles streamed to the surface. Releasing the built up gas lowered the water level nearly back to its starting point.