The only fish I know of that is called a celestial is a type of goldfish. If that is the case then most other fancy goldfish would be OK as companions provided the tank is large enough. A single goldfish needs at least 10 gallons of water to live reasonably well.
Salt Water Fish
No, you should not be putting material in with fish.
depends on the FISH. if they saltwater fish, then you put salt water in the aquarium, same thing for the freshwater fish. if you dont know what kind of fish it is, look it up.
You shouldent put a beta fsh with an oscer.
goldfish, koi
Yes this is possible. All requires on the medicine bottle should be followed. The diseased fish should be separated.
It is better for the fish to be put in water that it was found in.
non communal they should not be put with other fish
Generally the answer is no. The only reason the should be put in together is for breeding purposes and this should be carefully monitored as it can get out of hand. Male bettas will attack females.
A fish will most likely die if you put a cleaning agent in its fish bowl without removing the fish. You should remove your fish with a net and place it in another safe container until fish bowl is clean.
The Sun Fish and Star Fishes?
crayfish should be put in about the temperature of water you would put fish in.