How are you turning it off? If at all?
My DIY CO2 helped my tank a lot. But I had to turn it off at night or it would drive my ph way too low. I was using an internal reactor driven by a Power head. When off the CO2 burped up & out the powerhead.
It does work but many tricks need to apply for any consistency in ph & CO2. A digital ph meter tells what's really happening but the regency will pretty much ball park you & tell if your dropping or rising in ph.
I do feel that it is not healthy to burp the gas into the room. I was actually feeling very sick for awhile . I felt it was the CO2! I decided to run on pressurized & see what happens. I felt better almost immediately.