1. Remove the dead fish from the tank immediately.
2. If you have other fish in the tank, monitor them for signs of illness and be prepared to treat them if necessary.
3. Take the time to observe your betta's body. Look for any physical abnormalities or injuries that could have caused its death.
4. Flush the dead betta fish down the toilet or dispose of it in a trash bin. Do not compost the fish, as this can spread diseases to other animals.
5. Clean the tank and any decorations or accessories that the betta came in contact with. Use a mild detergent solution, and rinse thoroughly.
6. Replace the water in the tank, and add a water conditioner to remove any harmful toxins or chemicals.
7. Wait at least 24 hours before adding a new betta fish to the tank. This will allow time for the tank to fully dechlorinate, and will also help to prevent any potential disease transmission.