beta with white spot and stiff fins

Question
Dear Chris,
my betta didn't make it through the night.  I had a lamp next to it and a temp strip...he was at 80-81 degrees at all times.  when he died he had a spot on one side of hime that was brown and black in color that stretched to the other side of his tail fin and part of the dorsal.  i am just curious if you know what he had, i have never seen something like that before.  just to give people who own bettas a heads up if their fish gets the same illness...thanks for your answer.
~mary!
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Followup To
Question -
ok.  I have had my beta for about 8 months now and he has been ok.  He developed fin rot but I have managed to keep a handle on it.  But today when I looked at him he has developed a large white-ish spot at the elnd of his body on the left side.  and on top of the his fins are stiff.  he is still eating but i don't know forhow much longer.  I am fairly certain he does not have much time left, but i was wondering what he has, and will i be able to re-use my tank later if i choose.  thanks for your time.
~mary!
Answer -
Hi Mary;

He may need his tank warmer. Bettas get sick very easily when the water temperature is below 78. Many are kept at low temps in spite of these needs, but many don't survive that way very long. Their immune systems can't function when the temperature is too low.

To help him get well, change his water and slowly raise it up to 82 degrees. You might need to put a lamp close to it for extra warmth if you don't have a heater in the tank. Also, get a product called Melafix. It helps heal skin and fins and fights infection.

If he doesn't make it, just rinse the tank  and accessories with hot water and it should be fine to use again.

Hope he does though and feels better soon......

Followups welcome

At Your Service;
Chris Robbins

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Answer
Oh, that's too bad. Poor little guy.

It sounds like he may have had cancer. It could also have been a bacterial infection like an abcess that went all the way through his body.

Don't be afraid to try again with another betta. Just clean out the tank with hot water and it should be plenty clean enough to use. If you want to sterilize it you can add a few drops of bleach and let it sit for an hour or so. Rinse very well with hot water and let it sit for a few days. Make sure there is no bleach smell leftover and then use a good water conditioner before you add your new fish.

Followups welcome

At Your Service;
Chris Robbins