I have 2, 3 gal tanks, that holds about 2.7 gal with an undergravel air filter (one at work and one at home). I also have one live Anubias
plant tied to a rock in one of them (work) and 2 in the other (home), among all the other plant decoration in the tank and a small carbon filter sitting in the gravel (the ones that look like treasure chests). Is it really necessary to do a 50% water change twice a week?
The tank I have at home I do water changes every couple of days to remove the tannins that are leaching out of the drift wood.
I had a betta tank years ago, 2 gal I think and I did water changes once a week and didn't have any live plants, and Mr. Fishy lived for a number of years.