The setup, in plain numbers
Start with the home itself. The vet needs the pond or tank's size, how long it has been running, and what lives in it — just this goldfish, or companions, and if so, which and how many. Say how the water is filtered and how often you change part of it, and roughly how much. A goldfish in a small, new, lightly filtered tank lives in very different water from one in a mature, well-filtered pond, and the same symptom can point in opposite directions in the two setups. If the goldfish lives outdoors, note the pond's depth and whether it has shade, moving water, or a net against predators — all of which change the water and the risks the fish lives with.
The water's recent story
Bring recent test results if you have them: ammonia, nitrite, nitrate, pH, and temperature, ideally from the last few days rather than a single reading taken in a hurry that morning. Most goldfish health problems begin in the water, so a short run of results lets the vet see whether something spiked, drifted, or has been sitting wrong for weeks. If you do not test, say so honestly — the vet can test a sample you bring in a clean container, and knowing the gap exists is itself useful information. A photo of the pond or tank on your phone helps more than you would expect, because the vet can see planting, algae cover, and stocking density at a glance.
The fish's own recent story
Describe the change that worried you in order: when you first noticed it, what exactly the fish does differently, and whether it is getting better, worse, or staying the same. Appetite is a headline detail — eating eagerly, picking, or refusing — along with swimming posture, where the fish rests, and how it interacts with companions. Mention anything visible: spots, frayed fins, raised scales, unusual waste. Dates matter less than sequence; a clear order of events helps the vet separate a sudden crisis from a slow decline.
What changed lately
Vets ask this because so many cases start with a change. New fish added, a new food, a filter cleaned or replaced, a treatment used, a water change missed or doubled, building work or pond treatment nearby — list anything in the few weeks before the problem, even if it seems unconnected. For pond fish, add recent weather: heatwaves, storms, and ice all shift pond water fast, and a heron visit or a frightened, hiding fish tells its own story.
Why this history changes the treatment
With the history in hand, the vet can judge whether to treat the water, the fish, or both, and can avoid remedies that would crash a small tank's filter or clash with something already used. Without it, they are guessing at the most common causes while the real one — an undersized filter quietly overwhelmed as the fish grew, say — carries on at home.
Keeping this history is easier as a habit than as an emergency summary, and a running log of tests, changes, and appetite notes in your goldfish's Pet Passport on KinsLe means the whole story is already written down, in order, on the day you need to tell it.