Betta Dead - Suspected Fin rot/Columnaris

Hi everyone,

My poor crowntail Betta named Tassel passed away this morning. He was originally in a 10L betta tank for about 8 months. The filter wasn't working properly, which unfortunately meant the water quality wasn't the best for the last few weeks.

I bought a new 28L aqua one ecostyle for him last week and used bionoodles from a different established tank. As soon as I transferred him to the new tank (with better lighting) I realized he was sick - clear fluffy stuff on one bit of the tail. He also had a slight redness on the ends of some of his tassels.

Despite medicating with TriSulfa tabs (I suspected he had fin rot and maybe columnaris) he passed away. If someone could please confirm this that would be a great start. Please see photo attached - though you cannot see it he also had clear fluffy stuff (possibly fungi) on his head (but not his mouth).

Advice regarding what to do (and how long to wait) before purchasing fish for this new tank.

From what I understand I should wash the tank, sand and decorations with boiling water and buy new filter media (and seed with biological media from other tank). I also have hydrogen peroxide which I understand can also be used to disinfect the tank.

Any advice would be greatly appreciated.

The fish probably had ammonia and or nitrite poisoning, which damaged the internal organs and fins, and a bacterial infection got in and finished him off. Kind of disappointing because he is an interesting colour.

If he was in a tank by himself for 8 months and no new fish were added then it is not Columnaris.

Just wash the tank out with water and set it back up, wait a week and add a fish.

If you are concerned about diseases you can add a heap of salt to the tank (so it can no longer dissolve) and let it run for 24 hours, then rinse it out and let it dry for a couple of days. Then set it back up, wait a few days and add a fish.

In future if you ever get a sick fish or an unhappy fish, or if the filter stops working properly, reduce the feeding to once every 3 days and do a 75% water change each day until things are fixed. Poor water quality kills more fish than anything else and it's normally caused by too much food and lack of filtration. Don't worry about the fish starving either because they use food to move and grow and don't need food to stay warm (unlike people). Fish can go for weeks or even months without food but if you put too much food in the tank, you get an ammonia reading and the fish dies pretty quickly.

Don't worry about the fish starving either

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Someone once told me " A slightly hungry tank is a healthy tank " and its true especially with predatory fish, unlike aquarium fish they dont eat every day. Inactive fish like Bettas living in 5 gallons or less do not need a lot of food, 2 or 3 small pellets a day is more than enough.

Sorry about your fish.

Thank you so much Colin and Nick for your prompt advice.

Colin, yes he was in the tank alone for 8 months, no additions so I am guessing that it was a mix of bad water and bacterial infection (maybe fin rot). I might go down the salt route just to be safe. I will keep your advice in mind for future reference.

Nick, looking back on it now I don't believe I overfeed him (i.e. didn't give him food he wouldn't eat) but I definitely could still have limited the food more. I will keep that mind though.

Here is a picture of a healthy Tassel, to celebrate the better part of his life with you all.