If polution/rot has set in and the water has become toxic/poisonous, then the tank will need to be stripped down for a complete clean out and scrub. The living occupants will need to be placed in containers with good clean water of the correct parameters. If the overfeeding was recent, then the easiest way I know of is to remove the left overs with a syphon tube (hose) and simply syphon the rubbish out into a bucket or other container for removal. The replacement of at least 10% of the aquarium water should be done weekly anyway if you wish to have a healthy environment for your fish. Fresh water to fish is like fresh air to us. We need it to live.
a fat betta fish
If your fish food is staying afloat for a week it is most likely because it is just buoyant and you have overfed your fish. Feeding your fish less will reduce fish food staying afloat as well as help keep your fish and tank healthy.
in a tank or the ocean?
Then your filter is not on.
It dies
It will stink and make ur fish sick.
As long as that fish is in your tank, the other fish will benefit from it's special effect.
your tank was probably not covered. beta fish are very good jumpers.
There are several common reasons why betta fish may be dying, including poor water quality, improper tank conditions, overfeeding, and stress. It is important to ensure that the tank is properly cycled, the water is clean and at the right temperature, and that the fish are not being overfed. Additionally, make sure the tank is not overcrowded and that the fish have enough space to swim and hide. Regular water changes and monitoring of water parameters can help prevent further deaths.
Cut it up and eat it - put it out of its misery.
fish die of oldnesss or not well tanked care before you get a fish make sure you know fats about it and mostly get a tank with a filter. i had with that died now that i have a tank with a filternothing happens
they will die