I think what your tank is missing is fish or shrimp!
And since you seem to have enough equipment for a much larger tank, uh, why not get a 20L? THERE is where your HC would be at home. Or, even better (and my current wish list item), a rimless 33L 48x12x12!
So I got my 5lb Co2 tank refilled today and decide to take this picture. My faithful compact Co2 regulator, nearly one year of service and nothing went wrong. Stable bubble count, stable working pressure and best of all, it's BLUE!
Going to replace the 5 lb with a paintball set up and replace this regulator with a dual stage one.
I also found out that people actually use Co2 to grow *ahem, other types of plants. I thought the Co2 in the air was enough. People actually use Co2 in their *ahem other set up, they ask me a bunch of questions why I had a 5lb tank.
I would have to do a lot of explaining if someone never found the tubs of Dry white powder fertilizers, the API test tubes, the Co2 tank and the plastic container of HC Cuba I grow and the syringes I use to spot treat algae.
"..But Officer... this is all for the fish!..."
LOL, thought the same thing, then I found this comic!