PLEASE, do not just cut and paste and fill in informtion.  Instead, try to answer as a narrative such as "I have 3 fish in a 40 gallon tank.  It has an _ filter and 2 air stones."

LIST WATER PARAMETERS (ammonia, nitrites and nitrates)
Then, list all symptoms in order, when the symptom  started (days ago).
If poop is seen, describe the look (see poop diagnosis)

Possible symptoms- REMOVE those that dont apply
Died suddenly, floating, gasping at surface, yawning, scraping on things, jumping, sores (red/ black/ white/ gray/ fuzzy/ greasy/ shiny, dots/ patches/ wounds/ salt grains, streaks) on the (gill covers/ front, back or tail fins/ body/ head/ along the lateral line), wont eat, getting thin, bent spine, lethargic, darting, clamped fins, swimming funny (give details)/ head standing, tail standing, floating at the top upside down, sitting on the bottom, scales sticking out (base of tail fin/all over),  losing scales, bulging eye(s), fins are (shredding/spitting/rotting), changing color, lump(s) (solid, soft).

How many goldfish in the tank,  any other kinds of fish?
How many gallons is the tank?
What are the water parameters? (The levels of ammonia, nitrites, nitrates, pH and hardness or alkalinity readings in the tank and out of the tap?)  Which tests do you use?
How long has this tank been up and running?
What kind of filter? How many gallons does it turn over per hour? Is there charcoal or ammonia absorbing material used?
Does the tank have gravel, rocks, driftwood, anything else?  How much gravel, what kind and size?
List all conditioners, etc. routinely added to the tank.
What kind of supplemental aeration in the tank and is it run all the time?
What is the temperature of the tank? Is there a heater?
How often are partial water changes done, filters and gravel cleaned? Is the temperature of the new water matched to the temperature of the water in the tank?
What kind of food, how much, how often is it fed and where is the food stored?
Do you know about cycling a tank and the good biobugs?

Has anything new been added to the tank in the last two months (fish/ plants/stones/decorations/gravel)?
Where new fish quarantined and for how long?  Were new plants dipped?
Were filter components replaced in the last two weeks?
Has there been a temperature drop suddenly in the tank like air conditioner being used or a cold front coming thru?

List what percent  water changes have been done and when in the last 2 weeks.
List all medications used and how many treatments over how long a time for the last month.