I bought 5 gold fishes to my tank last week. It's 7 days now.. 3 have white spots on their tails. Iam really worried.. I cleaned my tank the plants everything.. And filled water 4 days before adding fish. What I have to do now.. Please help

Ami

They have Ich or "Ick". It is a parasite that Goldfish get and it will kill them if they aren't treated.

Ich Disease | Causes, Symptoms, Cure and Prevention (http://goldfish2care4.com/goldfish-diseases/ich.html)

Thank you for the answer. What I have to do now? Can you suggest any medicine?

Go to a pet store and ask for a cure for Ich.