Let's talk bubble nests just out of curiosity. While I was cycling my tanks they live in now they was living in heated non-filtered kritter keepers. Now they live in a 10/5 gallon tanks with sponge filters. They used to make bubble nests every water change in their kritter keepers. It never failed change the water next day a new bubble nest would be present. Now they haven't made a bubble nest in 3 weeks being in their main tanks. I know for a fact my blue Betta is healthier in the more stable cycled tank as he used to have chronic fin melting/rot and tail biting issues that are now cleared up. My red Betta is just a happy go lucky guy and healthy as ever with his tank. I'm using a sponge filter on one of the tanks and a baffled internal filter that barely causes any current as Cosmo can actually hover right under the sponge that is creating the baffle with no difficulty. The water checks out fine as far as parameters, temp is 78-80*, and currents should be minimal. Any other reason a Betta wouldn't build a nest in a larger tank?