Ive recently notice my Betta hanging around in one corner flaring himself at the wall. He has weird burst of aggressively n followed by flaring. He will then swim away they repeat over and over again. Why is he doing this?.
My guess is that the wall is very reflective, so it’s like a constant mirror. Since bettas flare at each other in the wild to protect their “territory”, this is probably stressing him out a bit… I saw something the other day where you can just take a non reflective piece of paper and tape it to the outside of the aquarium wall that he’s flaring at, that should hopefully fix the problem.
My bettas definitely have done the same thing due to seeing their reflection. Totally agree with the others recommendation about non glossy white paper. If you have a planted aquarium you can also try some plants.
My tanks are so reflective that no paper helped. If this is the same as yours, you can try more plants, as recommended above, or you can try lining some of the areas with Indian almond leaves, which is what I do (if you can stand the brown tinted water that tannins create). Bettas love the stuff, and it helps with stress and healing.
You can find some really big leaves, or smaller ones. I order mine from Amazon, but most places that sell fish should have them.