In my 200L aquarium I allow the CO2 to bubble into the intake tube of my external canister filter. I only use about 10 bubbles per minute and only very occasionally do very small bubbles come out of the outflow of the filter. This is sufficient to turn my drop checker lime green. The advantage of this method over using an inline reactor is that there is virtually no loss of flow. Hence my eheim 2026 filter rated at 950lph achieves a fairly respectable 750lph! Not trying to show off, just thought that this could be useful to other hobbyists!