My bubble counter is one I made from a syringe. It is the body of the syringe, with a plastic check valve stuck thru the plunger piston, which has the plunger stem cut off, and the check valve/piston glued into the body to avoid any leaks. The needle end is a good fit inside my tubing, but is clamped to be sure of no leaks. I would suspect leakage, but the rate of bubbles going up the counter just about exactly matches the burping noises from the rotor. Very obviously not nearly all of that CO2 dissolves into the water, but with a CO2 mist you don't expect or want it to. I will do a lot more experimenting and checking when I move everything into the bigger tank.

That tank will have a continuous water change system, and has about 50% bigger footprint, but the same length as the 29 gallon tank, and is about 3 inches deeper. Much better for aquascaping.