goldfish keep dying

Question
I have a pond that I have goldfish in. It is 10'x15' and approximately 2' deep at the deepest area. I have adequate aeration by way of 2 fountains a waterfall and a filter that returns the water back into the pond however I bought about 50 goldfish about 2 weeks ago and they lived for about 4-5 days then I found about 10 -15 of them dead all in the same day and every since then almost everyday I find 1-3 dead in the morning and then about the same every evening. I have examined the dead fish and there is no sign that anything has gotten ahold of them and hurt them nothing seems to be wrong with their scales or gills what else could be killing them? if an animal has gotten a hold of them wouldn't there be some kind of damage to their gills or body? Please help I would like to figure out what is going on. Thanks for your help!

Answer
Your pond is close to 2000 gallons (if it were mostly 2 feet deep that is).  That's about the size of my pond.

Is this a new pond?  Are there other fish in there?  I will assume it's a new pond and that these are new fish.  First, you added too many goldfish.  I suggest only adding a dozen or two at most at first.  My pond is 10 years old and has about 30 goldfish (after many spawnings).  Even if they're small, 50 goldfish is a lot.  Have you tested your pH, ammonia, and nitrite levels?  They may be off with so many fish.  Second, store-bought goldfish are often sick especially if these were feeder fish as I assume that they are.  Feeder fish (and some regular goldfish) are almost certainly going to be carrying at least one parasite, bacteria, or fungus.  For that reason, they should always be quarantined if possible and treated with anti-parasitic medications and antibiotics.  To improve the health of feeder fish or a sick batch of fish, I suggest aquarium or pond salt, MelaFix, Maracyn I and/or II for antibiotics, and something like Aquari-Sol for ick and other parasites.  

Since your fish are already in the pond, I suggest using the pond salt (0.01% solution) and MelaFix and perhaps a parasitic medication but only if you can confirm a diagnosis.  Your local aquarium or pond store or pond club might be able to examine the fish to find any possible culprits.

If there were a predator, they would most likely be in pieces or be torn up or at least bruised (septicemia or obvious blood veins).

So, test your pond's pH which should be 7 to 8 ideally and the ammonia and nitrite which should be zero.  Add pond salt and MelaFix. Try to get a diagnosis locally from someone.  Remove any dead fish promptly.  Do not add any more fish at least not until there have been no deaths in a month.  Try to quarantine any future fish.

Good luck!

Robyn
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