Originally Posted by Bettatail
get the super atomizer type.
This. Alternatively, you could get an in-line CO2 reactor for a little bit more if you don't want to see the diffuser and tubing in the tank. The CO2 mist will be just as fine, but you may find that disconnecting the filter tubing and soaking the diffuser is a pain. You may want to invest in an additional diffuser so that you can always have one clean one to swap in while your other one is being cleaned (I recommend this for all atomic diffusers, not just in-line ones).
Even more alternatively, you could build your own reactor. There are various different builds so you'll just have to read around and figure out which one best suits your needs.