My name is XXXXX XXXXX X am a Vet tech and fish keeper. I apologize for you having to wait for an answer.
Have you checked the water parameters? If so what type of kit did you use and what were the numbers?
Are there any red streaks on the fins or body?
Do you have filtration?
What size tank is your Goldfish in?
The test strips are very inaccurate and I always suggest using an API Master test kit. They are more expensive, but will give the best readings. I had a Gold fish yesterday that used the strips and everything showed normal. They did the test again after I recommended the test kit and found all water parameters were off, causing serious issues with their fish.
First let me say a gold fish should have a min of a 10 gallons of water per fish and preferably 15 gallons. What you have described with the loss of scales is caused by Ammonia burns. The Ammonia should be 0, Nitrites 0, Nitrates 20ppm or less and the PH 7.0. What I suggest is a 3/4 water change and use a dechlorinator and ammonia remover. In the new water, please add 1 teaspoon full of aquarium salt per gallon of water and some Stresscoat. The Aquarium salt will help heal the fish. It creates a slime coating on the body to protect it, fights fungal, bacterial, and parasitic infections and reduces stress. The last thing I suggest is some Nitrifying bacteria, to help restart the balance. You will need to retest the water daily and for about a week do 1/4 to 1/2 water changes. Do not add any more salt, but make sure the water is treated with the Dechlorinator and Stress Coat. This should help the fish heal. Water quality is a big part of fish keeping and if the ammonia, nitrites, nitrates and ph are off it can cause serious damage to a fish. Please let me know if you have further questions, my goal is to give you excellent service and to help your fish. Joan