Please help, this is cry 3, I think lol

Parameters, tested this morn morning Temp- 75 pH- 6.5 Nirites- 0 Nitrite- 0 Ammonia- 0 Gh- 0 Kh- ~20

Curts fins have been deteriorating for months, I can't figure out why, I need help please- he needs help. I've posted before on here about this issue, Curt, 1.5 year old male halfmoon.

10 gal tank, many plants, weekly 25% water change with daily spot cleaning, sponge filter, 1 nitrite snail, tank itself is over a year old, nothing that could tear his fins in tank, his personality is still VERY much in tact- he's not once looked I'll beside his fin situation. He's fed daily, I make sure he eats all pellets to avoid a bio load. I give him beta remedy and increased the tannins in the tank, but it's not working. Please help I don't want all of his fins to go, he's still so sassy and upbeat right now. He's around 1.5 years old from petco.