I'm hoping someone may be able to help or has encountered this problem before. I have a well established 1800 gallon pond. It consists of Gold Orfe, Shubunkins, Sarasa Comets, 1 small (3-4" Channel cat) and common Goldfish / Comets most of which were born in the pond over the years. Nothing new added this year. Wednesday we noticed one of our goldfish had died. I didn't think much of it. However, strange thing was there was not a sign of any trauma or sickness of any kind. In fact, it looked perfectly healthy except it was dead. Since Wednesday we lost 2 more on Thursday, 3 on Friday and about 5-6 over this weekend. Every one of them is a common goldfish / comet. I have not lost any of the other fish listed above. All the dead goldfish show no signs of sickness or trauma. They vary in size and the only symptom we see right before they die is they tend to start resting in one place and not swimming around. None of the fish are at the top gasping for air and most come swimming over looking for food. We have stopped feeding them as of yesterday.
I took a sample of pond water to a pond business today and they tested the water. PH was 7.4, Nitrate and Nitrite was next to Zero. The only thing that was very high was Hardness but the owner did not seem concerned about that.

He told me to add at least 1 cup of pond salt for every 100 gallons but he recommended 2 cups per 100. He also told me to use this product called ProForm-C for three straight days.

Does this sound like a good start? I really don't know what else to do. I don't know why only the goldfish are dying.

I have enclosed a photo of the latest fish that died. As you can see, nothing looks unusual on the surface. One other thing, I decided to open up a few of the fish that died. I didn't see any food in it and the swim bladder was fully inflated. The one thing I thought looked odd is the gills looked completely white. No color whatsoever. Is this normal for a fish that just died?

Thank you in advance for any help you can provide.
-Mike

The ProForm-C isn't be used with salt. I don't know what your salt level is, only what you added/plan to add. Formalin, part of ProForm-C, lowers O2 in the water and salt increases slime on the gills making it more difficult for the fish to take in O2. At some point these two issues can kill stressed fish. It's hard to tell what salt level in your pond would start killing fish.

Throwing stuff into the pond without knowing what problem your fish actually has...very good way to kill fish. When healthy they can take that kind of needless abuse, but when already stressed, it can be a real killer. It can be very difficult to figure out what the problem is, but for certain you get make a small problem into a huge problem.

Step 1. Water quality. If ammonia and nitrite aren't zero that's what you fix. You do nothing else. Fish, like people, can often recover if in a good environment. Fish immune system is the best tool you have for figuring out a problem and fixing it.

Step 2. Add an air pump. It's safe. It may not be needed, but if it does increase O2 it will enable the fish to better fight whatever the problem is.

Step 3. If water is cold, say under 60F, you can move sick fish to warmer water in a hospital tank. Slowly warming the water. Fish immune systems don't work very well the colder the water. Optimal I think is 75F but you'd have to check that.

Step 4. Try and figure out the actual problem.

Step 5. Treat the actual problem in a hospital tank.

If you can't figure out the problem or a hospital tank seems like too much hassle but you really want to dump something into the pond go ahead. Then go shopping for new fish.

Were there any pesticides sprayed around or near the pond recently? I did some reading about glyphosate (aka round up) after the railroad sprayed the tracks behind my house -the stuff can drift, and depneding on weather conditions, it can travel quite far, up to 2600 feet according to one article I read. Fish and aquatic life are particularly sensitive to this particular herbicide - the warning labels state this quite clearly - do not use around aquatic areas.