My impression is that is not too much. Almost impossible to gas a 26 gallon tank with a single 2 liter bottle. But the only way to be sure is to observe the fish for signs of discomfort.
Pro Tip: It'll work better if you "pre-diffuse" the co2 by sticking a piece of chopstick, or piece of regular cotton ball packed tightly into the open end of the CO2 line. This way the pump will have a steady stream of smaller bubbles to work with, instead of big intermittent ones.
It'll be a lot quieter, more efficient, and produce a much finer 'mist'
*Edit, posted at the same time, just read where you do have a piece of cotton in the line. In the video it doesnt look like it. The mist should be steady, not pulsed like that. Maybe need to pack it tighter?
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