Welcome guatam. What a shame what happened with your new tank. Glad to see you'll separate the sharks from the goldfish. Those aren't going to work together as tankmates.
Getting a liquid test kit is the most important first step no matter what the setup or stocking will be.
Given the dimensions you've stated, gautam, your tank holds 44.9 gallons (169.9 liters). And that's without adding gravel/sand, rocks, and other decor. To accommodate 4 fancy goldfish (by themselves), you are going to need a tank that's 60-75 gallons in size. If you decide to rehome 2 of the goldfish, this tank will still be small even for two fantails.. but a 55 gallon tank would work. The larger size you can set up, the better. Goldfish are very social and bond with each other. It's not a good idea to keep them singly or in pairs on a continual basis. When it comes to filtration, go with 10 times the tank size in gallons per hour. That means, you'd shoot for 550 gph on a 55 gallon tank, 600 ghp for a 60 gallon tank, and so on.
I'm happy to hear the white spots are going away and agree with the others that it doesn't sound as though you were describing ich. A mild bacterial infection is more likely, particularly as they were overcrowded (probably unfiltered), you didn't have a liquid test kit to evaluate the water quality, and they were kept with other incompatible species. We are most happy to help you with this, so please ask whatever questions you may have.
Wish you all the best of luck!
