it means they are most likely dead or going to die
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.
usually its cos there scared from traveling or there getting used to there new tank.
That depends on what you mean to say. For example, if you have one angel fish in the tank you could say "That's the fish's tank" meaning that is the tank for the angel fish. If you also had a couple of clown fish, you could refer to the tank as belonging to all three fish by saying "That's the fishes' tank." Slightly different spelling and punctuation
No. all fish need fins to swim. Or they would just stay at the bottom of the tank and die.
if its that mean put it in a separate tank
If the fish is a bottom feeder (catfish, plecos), the fish will search the bottom of the tank for food and possibly below the surface and will generally dwell on the bottom of the tank. If the fish is a top feeder (african butterfly fish), it will search the upper reaches of the water and possibly above the surface and will generally live in this area as well. Open water fish (tetras, rainbows) will generally live in the middle waters of the tank, but will search for food at all levels. A frightened fish will go just about anywhere as will a hiding or stressed fish.
Bubble eyed gold fish have to stay at one spot in the tank because they feel like they rule the tank kind of thing and they want to watch all the other fish
if its a betta fish they will do that sometimes. if it is tired it will sleep at the bottom (just to make sure its sleeping and not dead, tap the glass gently to see if it moves a bit) but it will go back up to breathe since they do breathe air if its another fish maybe its sick or it might want to make some bubbles with its mouth.
depends on the size of the fish, there might not be enough oxigen in a small fish tank.
Scoop all your fishes to another tank or tub of water and clean the fish tank just as you would normally without the fish
There are a few ways. I only know 2. 1st take the turtles out of the tank (put them in another tank) and get a wind shield wiper against the sides of the cage. OR get a bottom feeding fish. They will eat all the algae in the tank.
All your fish will die. My buddy dumped a six pack in there and they were all dead in 3 hours...dont put beer in a fish tank