Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Fish do not mind the pH swings because of CO2.
Here is one way to 'turn off' the DIY CO2:
Set the bottles on top of the light. When the light turns on it warms up the yeast, and the yeast produces more CO2. When the lights turn off the yeast cools off.
Not great, but something.
In a tall tank you may be getting some benefit from the increased circulation of the bubbler. If you stop using it, watch the tank to be sure things are still OK.