Betta Fish: fin rot or consequences of his antics?

My buddy’s fins are looking rough and I want to make sure I’m doing everything possible to help him be healthy.

Tank size: 10 gallons

Heater and filter: yes, 10 gallon sponge filter and 5 gallon bettaflo

Tank temperature: 78°

Parameters: ammonia, nitrite, and nitrate all at 0, pH 8.2 (used API kit)

Age of tank/fish: 6 month old tank, 5 months fish parenthood

Water changes: vacuum substrate weekly to every other week, usually means replacing about 50% of the water (treated with Seachem prime)

Tankmates: 5 Amano shrimp

Feeding: tiny amount of betta pellets morning and evening, occasional frozen bloodworms/brine shrimp, 1-2 days fasting weekly

Decorations: gravel substrate, live plants, mopani wood, had a betta tunnel but he’d get himself a temporarily stuck trying to swim over instead of through so it was removed (I suspect this is how he damaged his fins)

My parameters have never tested above 0 since establishing a cycle and adding livestock so water changes are primarily for aesthetics. Currently treating with Seachem stress guard and catappa leaves. Figured I’d give it a week and if there’s no improvement or his condition worsens I’ll try something else.