Hi, and welcome to Fishforums !
What kind of filter do you have ? how big are the fish ?
Goldies are notorious ammonia producers and until your tank completes it's cycle you will have to maintain a military spec water changes schedule. Feed the less you can for the moment. You can consider bacteria starters, but results are mixed with them. Duckweed is a great addition if you have strong light, they love that stuff, and it will help with nitrogen. But not anyone likes it.
Hard water and a turnover of at least 10x per hour is recommended to keep happy goldfish.
On the other hand the API test kit reports 0.25 ppm if there is Chloramine left in the water I use. You can wait a little to see if it climbs over 0.25 and it's really ammonia in the readings... If it persist verify that your tap water conditioner treats chloramine. You can also check what your city's water supply uses on their web page.
Keep the fresh water flowing and at some point when the tank establishes, it will slow down on it own.