Can you help me to recover my fantail goldfish

Can you help me to recover my fantail goldfish, past 4-5 days fish stuck to the bottom or corner of the tank. not moving much.

So i've isolate the fish yesterday into new tank, so my other fishes not get effected.

Moving to quarantine was a good idea, good move.
We're going to need some more info to be able to be any help I'm afraid, if you could copy/paste this template and fill in the answers, people will have a better idea of what's going on. Info for the main tank and probably for the quarantine tank too would be good. @Deanasue is the goldfish guru here, hopefully she can help


Tank size:
pH:
ammonia:
nitrite:
nitrate:
kH:
gH:
tank temp:

Fish Symptoms (include full description including lesion, color, location, fish behavior):

Volume and Frequency of water changes:

Chemical Additives or Media in your tank:

Tank inhabitants:

Recent additions to your tank (living or decoration):

Exposure to chemicals:

Digital photo (include if possible):

For anyone who gets a sick goldfish like this, test the water for ammonia, nitrite, nitrate and pH, and make sure they are all good. Then do a 75% water change and gravel clean the substrate every day for a week. Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

If there's no improvement after a couple of water changes, you can add some rock salt at a dose of 2 heaped tablespoons per 20 litres of water. Keep the salt in there for a couple of weeks.

This is basic first aid for any freshwater fish and will usually buy you some time to get help.