Betta finrot - will it ever end ?

[Remmy]

Hey guys
My brother has a 10gal with 1 betta and 2 cory's.
A few months ago the betta's fins started to rot, at the time there was also a swordtail in the tank, thinking that it was nipping at the betta's fins we took it out.
Time went by and the betta's fins grew back to their full length and looked quite healthy... but no! some time after (i dont recall how long, couple of weeks probably) they started to rot again, grrr! the swordtail obviously wasnt the problem
This is the 4th time that its happened now, whenever the fins grow back to length they start to rot again.
The tank recieves weekly 40% water changes and is fed sparingly, any idea what could be causing this?

 

[jparnell]

Tough call. I had the same problem.
Could just be stress. Do you have the filter going at full strength? Does he get along well with the cories? Are the cories infringing on his "territory"? Do you add salt to your water on a regular basis or do you medicate when you see the fin rot?

Lots of variables - most common tends to be stress. Substrate can have a bearing on it too though - if he hangs out at the bottom a lot, on rough substrate, that could be causing problems.

 

[ArkyLady]

Do you have plastic plants or any other rough surfaces that he may be tearing his fins on? Your water change schedule should be sufficient to keep the water in good condition, but testing for the presence of ammonia or nitrites (or even excessive nitrates) would be a good idea just to be sure.