Betta Fish: Fish breathing hard, advice welcome

Hi everyone, recently took in this fish from a friend. She got him around January. She did probably like 2 or 3 water changes in that time, when I got him the other day his tank tested high for nitrates but ammonia and nitrites were surprisingly okay. His fins look a little tattered but not horrid. Anyways I’ve only had him since the 23rd and I’m doing a fish in cycle, I’ve been doing 30%ish changes every day and testing it, my ammonia is pretty steady from .25 – just barely green until I water change, everything else is 0s. I’m using a sponge from my other tank and I’ve got a couple live plants, temp says around 76-77. He swims like he’s tired, kinda letting his body drift below him. He’ll take fast, almost panicked sips of air at the top while swimming around every so often but sometimes he just chills and drifts around like he’s somewhat comfortable. Or he’ll sink and start doing this heavy breathing. I’m not sure what to think, I’m paying really close attention to this guy because he’s really inquisitive and I don’t want my friends fish to die (she moved to school). When I took this vid I did a 50ish% change and I’ve just been monitoring him. Any advice?? Kinda lost