Help with betta fish tank?

Well I'm no expert but I've had my betas in a 2.5 gal with a divider. So that's 1.25 gal each. I need to get a filter because it will be easier, but right now I do 1/3 change once a week. I have a tank with a lid and a light, and they are happy with the temp. I think it gives them a slight variety bc it's a tall tank. I also have live plants that make the water healthier. I've never tested their water any other way then with a tester, but I don't bother. I think I do alright with fish. I've had this really fast feeder goldfish for like 4 years. They don't die on me. Another thing you might already know - don't overfeed them because they get constipated. I went out of town and had someone feed the one I've had the longest, and it was overfed. If this happens they can get swim bladder disease. But I caught it early and if you ever have a situation where your fish swims a little funny do this: put him in a shallow tank, I used the cup he came in filled 2/3 maybe, because he couldn't get up and down. Then I thawed one pea, and put it in there. The next day he was feeling much better because it removed the blockage.