Your Guppy Fish is losing his tail you put him in a separate tank with no fish should you do anything else?

Yes, make sure the water is changed regularly. The tail will grow back but will never be as good as the original one. There will be a reason the guppy has been loosing its tail. If the problem is fungus then you need to fix the bad water problem that is causing the fungus by changing the water regularly. If the problem is fin nipping by other occupants then you will need to separate the fin nipper(s).