Best thing is to use DIY yeast instead of soda and HCL.

Cheaper and easier to handle.
See the DIY internal venturi reactor design I have in the articles and DIy section.

Simply plug the powerhead running the CO2 into the light timer, when the light comes on, so does the CO2.

Otherwise the CO2 bubbles out the top and is not dissolved.

Simple on/off approach that does not require you to stop the reactor or biological prcoess for each source of CO2.

10 hours is a pretty good ideal time for lighting.

Close the blinds, or cover the tank with a towel etc and take it off when you get home later at night.

Regards,
Tom Barr