Andrey Tarasevich wrote:

Hello

I'm using a Penguin Mini Bio-Wheel on my 5.5 gal tank (one betta, three
pristellas).

Now I'm thinking about trying some DIY CO2 injection, since things seem to
be slowing down (I'm thinking about maybe using that Hagen's Nutrafin bubble
counter with a homemade CO2 source). However, I have some doubts about
whether the whole thing makes any sense as long as I'm using the
aforementioned filter. The filter's outlet is pretty much a waterfall and it
provides some rather intensive surface agitation, which will lead to CO2
escaping from the water.

Your suspicion is correct. When I replaced a biowheel with a canister filter, I
was able to reduce my pressurized CO2 bubble rate from 120 per minute down to 45
per minute and keep CO2 concentration the same. Since DIY CO2 output is fixed,
you will be losing a lot of CO2 with that filter.