What you have been told is correct. I use 2x two liter bottles on my 10 gallon shrimp/endler and peacock gudgeons tanks and they all do fine with it running 24/7.
There is no way to turn off DIY c02. I use a mini power filter to diffuse my bubbles , I could turn that off so the bubbles will be huge and go straight to the surface , but its a waste of time since the amount isn't enough to bother the fish/shrimp
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