Perhaps a temperature change causing the container to contract/water to expand? Maybe watch and see if the water level rises and falls depending on the time of day/room temperature.
It wasn't that. It stays at room temperature most of the time. It was the gases forming inside the dirt layer that was causing the level to rise. I poked the substrate with a thin stick (read: bent wire clothes hanger) and it released bubbles of gases.
Originally Posted by Knotyoureality
Gotta' admit, I've been tempted to try one of these--but I prefer at least some livestock, even if only snails, in all my planted vases and the low surface available for gas exchange (or air movement to facilitate it) knocked them off my project list for the time being.
As I said before, I noticed the snails kept hanging at the top so I did lower the water level and now the snails haven't been hanging out at the top since I lowered it so I suppose it's working now. Here's the current level -
cool idea! how do you do water changes?
I just took the tube off a water changer hose and used that.