Yes, if it's not done properly.
You need the water to be to the proper chemical composition and temperature/pH of whatever fish you have. If not it can easily die from stress.
no a water pump can not kill a fish
If the jar has water in it with the fish, you will kill them.
Yes, chlorine is harmful to fish and can kill them if they are exposed to high levels of it in their water. It is important to always use a dechlorinator when setting up a new aquarium or performing water changes to make the water safe for fish.
Yes, water that is too acidic will kill fish.
Changing the environment will kill fish because of pollution and things. Oil and petrol can be dumped in the sea and this can be harmful and they die.
It depends on if you are doing a complete water change or a partial water change. I usually just leave the fish in and siphon off about half of the water than replace the water. The fish get a bit nervous but seem to be fine with being left in the tank. To answer your question: No, you do not have to remove the fish when changing the water.
When you are changing the water in a fish bowl, you have to empty cup ot bowl with water in it. Then, put it into clean water.
Fish vomit from changing water conditions or from eating something bad.
See the vet and fast
unhealthy water to have can kill from choking
well yea its could kill fish but some of the exhaust push the water really hard so the fish well go with the water and well not get killed
yes they can because they are water fleas