Betta Fish: I think my betta has a swim bladder issue, what else should I do?

Tank parameters taken today
• pH 8.2 (the tap water where I live is hard unfortunately)
• Ammonia 0.25 ppm
• nitrite O ppm
• nitrate 5 ppm
• 79° F / 26° C

I noticed my betta was resting a lot at the bottom of the tank the day before yesterday, I didn't really think anything of it and thought maybe he was just resting every time I happened to look.

Yesterday I noticed the same and did a 50% water change and added some Seachem stress guard but he seemed pretty sick to me 😞 I wasn't sure he was going to make it.

Today he's still resting a lot but seems perkier and more responsive to me. He's been trying to eat when I feed him but he's having trouble swimming and floats sideways and then back down to rest at the bottom of the tank.

Today I got some aquarium salt and added 1tbsp to a cup of his tank water, dissolved and added it back in. I also added more stress guard today.

What else should I do? What should I keep doing? Thank you in advance for any advice!