the best action to take with goldfish is to do nothing. just stop feeding. they will be fine. that stops the nitrate cycle from growing and helps you stabilize your pond over time. you simply need time to let the pond mature. there is enough food already in the pond to feed the fish, especially if you have plants. we just left our pond for 8 days when we traveled, and the 57 fish were just as fat and fine as when we left. algae is about 70 percent protein and is also a marine protein which is better for fish anyway. the nitrosomas and nitrobacter colonies just need time to establish. nitrobacter wont begin to develop until maybe 6 weeks after ammonia begins to be converted to nitrites, and nitrite is their food. as the colonies build, your pond can remove chemical waste just fine. the most important step in establishment is to provide lots of oxygen exchange. overdo it. we have a member with a championship pond who has his pond so heavily supported with air that you can't even see the fish for the bubbles. that sounds extreme but there is real science behind that method. our pond doesn't have that level of obscuration, but i have two alita air pumps running seven air stones in addition to four waterfalls. the more aerobic your environment the less anaerobic it is, and an anaerobic environment is what promotes bad bacterial growth. test for ammonia and pH, add baking soda so that the water is at 7.2 or so, and enjoy your fish. the pond will take care of itself. when the ammonia approaches zero, start feeding again. its easy.
