My CO2 reactor was inspired by this here:
I did it using a filter (prefilter) used in the system of osmosis (but this isn't my photo, I show for example):
Co2 is fed by tube visible in the picture.
The filter can be used also for biological filtering and can be filled with ceramic cartridge, which will also reduce getting the undissolved CO2 into the aquarium (in the form of air bubbles).
I use this reactor because it can dissolve the CO2 with 100% efficiency without any loss. I have a small bottle 1.5kg, and I give a lot of Co2 for 2 tanks, if I had big losses I would have a monthly refill bottle, but on this way I do it every 3-4 months on average. And this is the main reason. I lived in Poznan 7 years, now I changed my place of residence and moved to a small village. The Big Theater (Teatr Wielki) is in Warsaw.