Sudden Death

Question
I have a landscape pond that I have goldfish. I have had some for almost 8 years. I probably have more in this pond then I should but I have never seen the fish gasping for air, etc. Our weather has been in the mid 90s for several days and I started noticing that the fish were lying still on the sides and bottoms more than normal. Today they stopped eating and have have lost two of them, one being the oldest. Looking at him physically he seemed normal, no noticable disease. I worried about lack of oxygen so I immediatedly started adding water and stirring up the surface and I noticed that the fish became very active, even a couple of times jumping out of the water surface. They seemed better for awhile. I added a airstone and started pumping in air with a pump. What do you think could be the reason for this acute onset of demise? What should I do? I worried that I may have added too much de-chorline solution so I added some water to the pond to dilute any possible poisoning issues....help?

Answer
Certainly low oxygen levels are a concern in this heat.  I've lost half a dozen fish in the last 3 weeks with no symptoms.  I suspect oxygen and the extreme heat at least played a part even though I have two waterfall systems and recently put in my air stone too.  I would have suggested water changes and an air stone but you've done that.  You can also shade the pond with an elevated tarp if there's not a lot of plant cover.  Conversely, too much plant cover inhibits gas exchange so if you have a lot, remove some.  How much of your pond's surface is covered?  Dechlorinator is pretty safe even at a double dose.  I suggest water changes anyway to bring down the water temperature and in case the water quality has suffered.  Check your pH, ammonia, and nitrite to see how they are doing.  If you can get an oxygen test kit, you can see how the oxygen levels are.  I can't find mine but my boss is going to test my pond water here at work soon.  I hope both our ponds make it through this horrible heat!

Robyn
fishpondinfo.com