There could be several reasons why your fish is sinking to the bottom of the tank. It could be due to a swim bladder disorder, overfeeding, water quality issues, or a health problem. It is important to monitor your fish closely and consult with a veterinarian or a fish expert for proper diagnosis and treatment.
Fish do not normally "float around" they swim. If your fish is floating/sinking then it is probably dead.
The swim bladder
they just settle at the bottom of fish tank
gravel
A fish sinks to the bottom of the tank because its body is denser than the water, causing it to be pulled down by gravity.
I suggest that you learn more about your fish in your aquarium. One of your fish might be a bottom sucker which means that they eat all of the dirt on the side or bottom of your tank. If one of your fish are bottom suckers, that's probably the reason why your aquarium is clean. If none of your fish are bottom suckers, than somebody must be secretly cleaning your tank for you.
It dies
Certain types of fish, such as catfish and plecos, are known for cleaning the bottom of a tank by consuming algae and leftover food.
Fish eggs, fish sperm, mold.
food flaots
You simply take any fish and drag it to the bottom of the tank and then drag it up (fastly) and it will go soaring!
If your Cory catfish is in a tank with no other fish species, it really doesn't matter. If you have other fish species with it in a tank I would try turning off the lights at night and feeding your Cory then. It will give your Cory a better chance of getting the food before another fish gets it because corys don't use their eyes to find food, they use their barbles.