I think he meant 1 bubble every 3 seconds, that's what I add to my 20 gal tank.

You could use more plants, some foreground plants.
A canister would look better and be easier over time.
the spray bars help a lot and the water level is less critical.

I like the Via Aqua brand, every bit as good as Ehiem and about 1/2 the cost.
Some like Rena, some like Ehiem etc.

Get the mid sized version, 200 gph size.

The power head you use for the CO2 need not be larger, just the filter flow blasting the current around can improve things for you.

Regards,
Tom Barr