Betta has white fuzz and a pit by his tail

[Jolyneeee]

I had this betta for a year (from petco). I change the water every week. Its in a five gallon tank and I change one gal per week. I feed him once a day and I did not notice this until now. He used to have a Nerite snail tank mate who passed a couple weeks ago. He's very aggressive and flares at me and his reflection no matter what I do.

He has something eating away his tail and his body, he has developed a crater and in the crater there is a little bit of white. I checked my water and my pH is 6.6 (which it usually is). 0 ammonia or nitrites. 5-10 ppm (the color variation on my test is a little ambiguous).

The picture was hard to get through the tank but IRL you can see that it is not something on top of his skin, it is a crater that must have spread because it was not to this size last week.

what is this? Does anyone know what i should do to treat it?

Edited July 28 by Jolyneeee

[Colu]

If your nitrites are 5 -10ppm that very toxic to your fish  I would be doing daily 50% water changes add 5x the amount of prime to help detoxify any nitrite till it constantly stays at zero that looks like body  rot when it spreads to the body can kill very quickly i would treat with a combination of kanaplex and jungal fungus clear fizz tabs containing nitrofurazone following this treatment plan combination of two provide a broad spectrum antibiotic treatment @Jolyneeee

[Jolyneeee]

@Colu

sorry I misstyped the original post because I was stressing . I have 0 ammonia and Nitrites . I have 5-10 ppm nitrates. I know this is not the best thing, but i heard fish can live in water with more nitrates. Even with greater water changes I’ve never been able to completely bring down the nitrates for some reason. There used to be plants and a snail in this tank but there isnt anymore and i do not generally leave food behind. 

[Colu]

On 7/28/2024 at 11:33 PM, Jolyneeee said:

@Colu

sorry I misstyped the original post because I was stressing . I have 0 ammonia and Nitrites . I have 5-10 ppm nitrates. I know this is not the best thing, but i heard fish can live in water with more nitrates. Even with greater water changes I’ve never been able to completely bring down the nitrates for some reason. There used to be plants and a snail in this tank but there isnt anymore and i do not generally leave food behind. 

10ppm of nitrate fine I would start treating as soon as possible with the medications I recommended