I'm treating him for infection. The vase is a gallon, I am very busy to do 3 water changes a week. I never had this problem with one of my older bettas which lived in a gallon vase for 5 years. Test kits are not cheap where I live and well I don't know how to use them.
I'm not sure what to tell you. You asked why, we gave you the answers. They deserve the best quality water you can give them. It doesn't take but about 10 minutes or less to change the water on a couple of vases. The test kits are not cheap, right, but they are an extremely valuable tool to fish keeping. They come with instructions that are so very, very easy to follow. Not a big deal really and well worth the $30 investment that will last a few years (as said above). It will be something you could use on all your tanks, not just the betta vases.