Act Immedietely

True fishes are very sensitive and they have to be quarantined to prevent other fishes from getting infected.

What you said is perfectly true. Always separate sick fishes, as they need special care, attention and diet to get better. Examine the reason for their sickness and provide suitable antibiotic course. Check the ph level of the isolation tank and see if the water is aerated optimally and also check for the water temperature. Your fish will get better soon and you can release it to your main tank again.

Not only that a quarantine is necessary so that any sickness that the infected fish is carrying does not spread to other fishes in your tank.

My spouse's dad had to do this, one of their fish got sick and they obviously didn't want the illness to spread to the rest of the tank.

This is very true and can not be stressed enough I do not feel.

It's not always easy to tell if a fish is unwell and may have some kind of disease which runs the risk of any other fish in the tank also catching the disease and falling ill as well.

If you do notice any of your fish are unwell ensure you remove them from the tank and quarantine them as soon as you can so that it does not spread.