Hain

I know nothing about fish but I recall most of my chemistry.

Do you live in a city? How are you purifying your water?

Cities often have chlorine and fluorine in their water supplies, which can be removed if you let the water sit for half a day in the sun. Other cities, like Milwaukee, actually put calcium hydroxide, Ca(OH)2, in the water to make it basic to prevent the decay of the unknown amount of lead pipes under the city. Ca(OH)2, being the active ingredient in most antacids, is safe for humans to ingest, however really bad for plants and most likely fish.

Recall that goldfish are freshwater fish, and that water softeners use salt to replace heavier metal ions, like calcium (Ca) and magnesium (Mg), with sodium (Na) since that is easier on pots, pans, pipes, and hands, but less friendly to your Goldie.

I agree with checking your pH.

I recommend you search Google on tips to care for your goldfish, since you know more than us on the specifics of your home and current methods of care for the goldfish.