Betta Fish: Mass forming & fin rotting :(no

5 gal. Heated & filtered.

80F. 8.0pH, .15 ammonia, 0 nitrite, 20 nitrate. API Kit

Tank Nov 2024. Fish April 2025.

Weekly 25% changes with siphon.

2 Nerite snails.

3-4 tetra betta pellets.

https://preview.redd.it/vtx88d72kyuf1.jpeg?width=3024&format=pjpg&auto=webp&s=12d758fe8b67c5625998d90b55e6cd2442a7face

I hope you mean 1.5 ammonia? Either way, that’s still higher than you’d want. I’d do a bigger water change stat, try to bring that number down. Also test your tap water to see if it has ammonia in it as some places have that issue as well. 80 degrees also seems to be a bit on the warm side, not just for your betta but also your snails (especially your nerite, a cold water snail who thrives in mucu cooler waters). Try more of a 77-78 range if you can adjust your heater. Without seeing the mouth growth more clearly it’s hard to say, but Bettas (blue morphs especially) are prone to tumors due to poor breeding, just keep an eye on him and if it seems to impact his eating. See if you notice improvement with these changes before trying anything else.

Others will suggest getting the nerite in a tank environment with tank mates that live in similar conditions but we’ll just focus on the immediate issue right now of your fish!