My tank is about that size. I use pressurized CO2 and don't regret it in the least. It is not overkill. I tried a Fluval 104 filter for a couple of months or so and didn't like the constant problems trying to keep the inlet open - debris, snails and leaves kept clogging it. And, the flow wasn't sufficient to keep up a good circulation of water. So, now I use a Maxijet 600 powerhead with a sponge on the inlet, with my CO2 tube stuck thru the sponge into the sponge support grid. I get a good CO2 mist throughout the tank, good, if not too much circulation, and no worries about clogging. After about a month this is working very well. I wouldn't try this with DIY CO2 because the extra surface movement does dissipate CO2, causing me to just about double my bubble rate to keep up.