Hey there. Welcome to the forum. I'm relatively new myself but have found it to be a wealth of knowledge. I have just started off my own 5 gal nano. I too wanted co2 so I put in the fluval mini 20g. It's a handy idea but the trouble is the reactor for me was too big and bulky. Plus the refills are a little expensive. I think I paid £14 for three refills. Which doesn't seem too bad but they do run out fairly quick. I also had a few issues with the valve leaking. Fluval replace them so it's not too bad. I quickly upgraded to a refillable setup and just kept the mini 20 for back up. It's way cheaper in the long run doing that. Hope this helps.