Have you tested the water? Is the weather very warm? Do you have an air bubbler going? We need more info.

As sleepless said, we need more info, but for a start, there can be a number of reasons: poor water quality (need to test the water), electrical shortage, bacterial infection, etc. Lots of options.

If you put your hand in the water and feel a tingle, it is electrical. I throw this idea out because a friend lost all her fish due to a short in an underwater light. She didn't realize that was the problem until she touched the water.

Good luck!

The water didn't make my hand tingle so I think we're OK in the electrical short front.

Would this test kit (see link) work for testing the water or would you recommend something else?

Thanks much!

Here is a link that might be useful: Quick Dip Complete Water Quality Test

I just read that the API Freshwater Master Kit seems to be a good one. I'll pick one up tomorrow.

How big is your pond and what kind of filtration do you have? How long has the pond been established? Are you doing water changes?

This sounds like a problem with water quality.

Start with water test. Do nothing else to start. In order of importance; Ammonia, Nitrite, KH, GH, pH, temp. The KH and GH is sometimes combined into an Alkalinity test. You may also see General Hardness test which isn't very helpful.

You really want to take several tests as pH can vary in a daily cycle. Test as close to day break as possible and evening /afternoon. A serial of test results paints a bigger picture. It also confirms if you're testing correctly.

The strip tests are not good in this case. They should only be used between better tests just to get a quick update to double check something isn't way out of whack. More of a test to see if further testing is needed if that makes any sense.

The reagent type tests (drops) are better imo for a serious test.

You can also take a water sample to many pet stores for testing although you have to be careful handling the sample, the container it's in. Things like pH and even ammonia can change a lot if the sample is shaken, heated in sun, etc. Swimming pool supply stores also have good testing for some parameters like pH and KH, better than pet stores I think in general.

Seachem has goods test kits imo. One of the few kits that can tell the difference between safe ammonia and toxic ammonia. Most only test total ammonia.

are there any parasites on the fish?
net some fish and get a good look at them.

Thanks for all of your great advice! I really appreciate it.

By the time I tested the water, everything tested as it should. The fish look fantastic and the water is so incredibly clear that I can see the tiniest pebble at the bottom. I've had the pond for 8 years now and the water has never been clearer.

In all that time I've only had one pump: Pondmaster 700gph. Except for a few months this winter (into early spring), the pump ran 24 hours/day, 365 days/year. Wow! What a great pump. However, it was hard-wired so it took a while for me to get my butt in gear and replace it.

The pond froze over a few times during the winter and the few months of no water circulation seemed to have really affected the balance.

The pond is not very large. We're talking only about 4 foot by 8 foot kidney, flat-bottomed, 30 inches deep, vertical sides. The pump sends the water to a small settling pond (2 feet diameter by 2 feet deep) which spills into another settling pond (1.5 foot diameter by 1 foot deep) which then spills into the main pond.

I have one plant in each of the 2 settling ponds (variegated rush and water arum) and I clean the gunk/sediment out of the bottom of the settling ponds once or twice a year. The roses LOVE it!

There are only a few plants in the main pond which includes 1 water lily, 2 anacharis bunches, 1 watercress bunch and 3 plants raised up in the center of the pond in a grouping (variegated japanese water iris, creeping jenny, dwarf corkscrew rush).

It seems that 6 fish is the maximum for my pond. They're all pretty small and I'm not going to push it. That number is fine by me. The fish eat what they can as I only feed them on occasion (about once/week). They're mainly goldfish varieties.

I only wish the 2 frogs would come back. I have no idea where they went, but there have been no frog sightings for 4 days now. :(

Thanks again for all the suggestions/advice! And please, no hater messages from people who think that if you don't feed your fish, you're some kind of horrible monster. Yikes!

The parts of tail and fin coming off your fish sounds like 'fin rot' and that is a bacterial infection. I had it bad for a brief time a couple of years ago. My biggest Koi (a butterfly) was literally losing pieces of her tail and fins just swimming.

I had to purchase a special bag of food that I fed them (all the fish) exclusively for 14 days. It was laden in some sort of anti-biotic anti-fungal stuff. It worked. Fish responded very well, and began regenerating all of their fins and had fully recovered within a month.

Then I accidently killed all of them by inadvertantly leaving the hose on for a few hours. Apparently killed them with an overdose of chlorinated water.

That was awful.

Oh man! That does sounds awful. Thanks for the information. If I ever have this problem again, I'll be sure to check out that way of administering the needed medication.

I've gotta say, the fish look great. Already, I can barely notice there was ever a problem with their fins/tails. They've regrown so quickly. Amazing.