I have a "level" in my tank that I watch. When my water is just touching the base of my light mount bracket we're good, when i start actually seeing the bracket it means that the flow is slowing down in the overflow tubes because air is accumulating. Pick a spot in your tank and you can either mark the glass or just have something that is easy to tell if the water has changed - usually it's only going to be about 1/4" to 1/2".do you mean inside of the physical box inside the DT or the water level in general in the DT.
do you have a picture of a marking to represent, im 100% a visual learner lol



