If you still have the dead fish, can you look at it's gills for me? They will be very pale since the fish is dead but the color should still be even. Look for white blotches, dead patches, goopy mucous. Also do you have a water test kit? If not....get one and check the pH, kH, ammonia and nitrite levels. The tons of rain makes me think of a pH crash right away. Don't add anything to the pond to fix pH yet though, because if your ammonia levels are going up, adding a pH buffer right now can make the ammonia much more toxic. Lets see what's going on before you add any chemicals to the pond.

don't worry about the critters in the skippy....they are not the cause of this problem.

Gills looked an even dark pink color throughout, they were not pale (but I had put the fish in the freezer). I can post a pic if needed.

Alkaline 8.4
Total alkalinity - between ideal and high
Chlorine safe
Hardness - very hard (always very hard here)
Nitrite safe
Nitrate 0

How about ammonia and pH? And how old is the test kit? Is it a drop kind of test kit or strips? Strips are not accurate. You really need to get exact numbers, not just safe or ideal.

Ph 8.4
Alkalinity 220
Chlorine 0
Hardness 425
Nitrite 0
Nitrate 0

I don't have ammonia, and it is just a dip strip, although it is new. I will go to the store and go get a drop test and update the info as soon as I get it.

Here is a shot of what the gills looked like:
{{gwi:207932}}

OK, I got the Aquarium Pharmaceuticals Master Test Kit. Results are:
High Range ph 8.4
Ammonia .5 ppm
Nitrite 0
Nitrate 0

Your pH is pretty high but acceptable. Normally an ammonia reading of .5 is not bad, but since your pH is high, that level of ammonia can be bad. Attached is a link to a chart that shows the relationship of pH and ammonia. At a pH of 8.5 and an ammonia reading of .5, you are in a danger area. I am not sure it's dangerous enough to have killed the fish, but still somthing that needs to be addressed. Don't lower the pH though. messing with pH is very stressful and since your kH and hardness are so high, you won't be able to stabilize it low....so just leave it alone. Your temp is low enough that you are probably ok, but just barely. But do get some ammonia binders in there such as ChlorAmX or Pond Prime or something like that.

so back to the fish. How are the rest acting? sitting on the bottom, clamped fins, milky looking, gasping at the top? Any symptoms you see are important. Any new fish lately? The plants could have brought in parasites, but since your water is pretty cool it's going to be harder to treat for them.

Here is a link that might be useful: ammonia explained

I forgot to mention something else too. Your photo of the gills is good. I am glad you saved the fish so you could do this because it helps a lot. the condition of the gills rules out a couple of things in my mind. Koi Herpes Virus makes gills look really nasty and also usually hits in warmer water. Costia...same as KHV....nasty gills although possible in cooler water. Ammonia burns shows up as white blotches on the gills. So it's possible this is related to the temperature swings, but not for certain.

Nothing to add other than I'm very sorry you lost your fish. I know how sad it can be.

Thanks for the ammonia chart, I'll save that.
The other fish are hanging out on the bottom. They sluggishly swim if disturbed, but they have been hiding out all day. They usually come up to the top when they see us, but I have really had to look for them today. I just nudged one with the end of the net and although the water was not quite clear enough to get a good view, I am going to say the fins were clamped. It definitely did not dart off as usual.
The water temp is up to 62. The pond heater didn't really run today, but we had a hot day (finally) and the temp rose a little.
Based on the test info I have saved over the years, the Ph is pretty consistent.
I am going to head out for some Ammonia binder right now.
Thanks for your help, any other thoughts for me? Do I just pretty much cross my fingers at this point? I've had these guys for 11 years, I would so hate to lose them.

I got some Aquarium Pharmaceuticals Ammo Lock and dosed according to the directions.
What do you think about adding Stress Coat and/or Stress Zyme?
Does the reddish leaking from the anal opening mean anything?

I'm not a big fan of stress coat for sick fish. It makes fish develop a heavier slime coat, but that also applies to the gills, making it harder for them to breath. What brand of test kit did you buy? some test kits read bound ammonia as if it is still there, and some only read the unbound ammonia. So in other words, one will tell you that you still may have an ammonia problem after you already fixed it and one will tell you only about the ammonia that is still a problem. Still...there are pros and cons to each. Here's a link that goes into a lot of detail about that.

The way the fish are acting makes me think that they are unhappy about the ammonia. Clamped fins and being sluggish are both signs of that.

so find out what kind of test kit you have, see where you are with the ammonia and then see if the fish are feeling better. Hopefully they will be. If not....we will have to explore this farther. Some salt in the pond will make them feel better, but lets hold off on that for now. Salt can't be used with some parasite treatments and I'd hate for you to salt it and then need to treat for something else.

Here is a link that might be useful: test kits explained

It's an Aquarium Pharmaceuticals test kit. It is a Salicylate reagent type test. The ammo-lock (same brand as the test kit) says a test will still show positive ammonia even after treatment.
I checked the fish this morning. I only saw a couple of them, but they were not on the bottom this time. I just saw one swimming so I went to check on it. It's the only goldfish in there, it's a white one and is about 6 inches long. It's fins looked pretty red. Is than an ammonia issue too?

I am not familiar with Ammo-lock so I googled it. Apparently it's strange stuff and it confuses most ammonia tests. So I guess you really have no way of knowing if the ammonia is bound up or still harmful. I don't think I'd like using a product like that when there are others out there that don't confuse a Salicylate test kit. At any rate, yes...the red fins can be from ammonia. I am still not 100% convinced that ammonia was the real problem though. But without seeing the fish and looking at a sample of the slime coat under a microscope, diagnosing parasites is impossible. It's possible that parasites could have come in on the new plant, but there is just no way to know. The plants came from LiveAquaria, a branch of Drs Foster and Smith. It's not like they came from someone else's pond where there were fish living. The plants were probably not kept with fish so I really doubt they were the source of the problem.

I think I'd consider raising the salt level in the pond. I normally never keep salt in a pond and prefer to save it for when the fish need it. This might just be one of those cases. It helps them overcome stress really well. Over the next couple of days, raise the salt levels to 0.3%. To get to 0.3%, you will need to add a total of 2.5 pounds of salt per 100 gallons. Add it over a 3 day period. That, along with the ammonia binders should make them feel better. Lets hope so anyway!

Thanks so much for all of your help!
I just heard my biggest fish do a nice fin swish when I leaned over to look in the water. I'm taking that as a good sign.
I was pretty much going in blind when I bought the Ammonia binder. The only place to go around here is Petsmart. They had several different ammonia treatments, but not the exact ones you listed. I figured if I stuck with one company's line, it would be better.
I am considering myself very lucky that in the last 11 years I have never had a fish die. I need to do some more studying up on Koi, I have felt so helpless here.
I will get going on the salt. Thanks again!

Glad I could help. I hope things have tuned around for you! The hardest thing about koi is having one get sick and not having a clue how to help it. Been there, done that. It's NOT fun at all. They can't tell us what's wrong...we just have to rule out one thing after another until you reach a logical conclusion. And even then....we are still often wrong.

I admire your persistance. Many people wouldn't bother making special trips to the store for test kits and chemicals, but you did and I admire that.

cindy

OK, the fish have perked up as far as not being so lethargic anymore, but now they are flashing and jumping out of the water.
The one that I get the best view of is still the white goldfish. I took a picture of it to show you how red the fins are.
{{gwi:207934}}

So, do I have a parasite on top of all of this ammonia issue? Should I do a partial water change (for the ammonia situation) and then keep adding salt? Shouldn't the salt help with parasites, or would that be a bigger dose.
What should I try next?

That same fish as above was hanging out near the surface today and it has lots of white dots on it, so now I've got to treat for ich too. Will this never end? Should I just stick with the salt or get ich medicine? The bigger fish are a little more active today, I did not see white spots on them when they swam near the surface, but they are still occasionally jumping.

Ich is one of the few parasites that is still controllable with salt. Since you already have some salt in there, I'd continue with salt for Ich. The bad news is if you have plants, they will not be at all happy with the salt levels required to control ich. You need to bring the salt level up to 0.6%. If you have to do a water change, replace the salt that you lose from the water change. Keep the salt levels at 0.6% for 14 days and the Ich should be all gone.

0.6% salt is 5 pounds per 100 gallons. You can use the Solar Salt in the blue bag, sold in the water softener department at Lowes.

Everytime I see that little guy, the situation gets worse. The ich is covering it's eyes. Should I just put him down at this point? I just don't see how he can come back from the red fins and the amount of ich he has. If I were to do so, what is the best way?

If you want to put him down, the best thing to do is get some clove oil (health food store or pharmacy will probably have it). I use 8 drops per gallon to sedate a fish for injections, etc. To euthanize him, use 15 drops per gallon of water. Put him in, cover it so he doesn't jump out and leave him alone for an hour or so. But I'd try the salt first. Since you are dealing with a bad case of parasites, get the level to .3% today and raise it again tomorrow to the full dosage. He might not survive it, but he also might.

I put the goldfish down, I got him into a 10 gallon tank so I could really get a good look at him. This formerly white/pink fish was brownish/orange all over. You could see every capillary around his scales. His eyes were totally covered over with who-knows-what. I just felt so bad for him, I though the best thing for him was to let him go. I don't like doing that at all!
I've been testing my water every day or two. With the drop version of the tests, the ammonia, nitrites and nitrates are all at zero. The pH is 8.2.
How long do you think it might be before the fish start to actually feel better? They are still hiding out in the shady part of the tank. I put some plastic over the end of a large diameter white tube so I could get a peek at them. Of the ones I can see (dang green water!), it looks like their fins are not clamped down but they are still just hanging out in the corner. I feel like we have turned a corner, water quality-wise. I'm just wondering how long it will be before my fish are happy again.
Go figure, but standing outside worrying about my pond and fish hasn't made it all better yet. :)

The issue you describe is a lot like I'm going through right now and I also live in Utah so I'm starting to think that it is our strange weather. I did a 25% water change twice last week and the fish will at least come up for food now but otherwise they stay at the bottom of the pond. Also, since the water change I am back to green pea soup so I can't even see past the top 2 inches. I thought I was going to loose them all about 8 days ago. They were gasping for air and falling to their sides. I put a extra bubbler in the pond along with the waterfall on full blast. Everyone is still alive for me so don't loose hope.

My water is testing normal on all counts now, but I have got that pea soup going on too. It just won't go away, grrr!
My fish seem to be feeling better. I see them swimming around and they have eaten a little bit of food. Three of them look great but the fourth Koi, a white one, has a big sore on her side so I am keeping an eye on that. I'm feeling pretty good about their survival now.
I wonder if it really was weather related, I'm in Utah County, how about you?

I am in West Haven (Weber County). I bought a uv light from a ponder in Davis County last Saturday and she said she's had a fish die every day for a week. Another reason I think it's the weather or even the heavy rain we had earlier this month. Maybe there was something in the rain. Now my pond is clear after only 5 days of using the uv light and all my fish are acting a lot better. 2 are still not feeling that great but they are eating so I think they will pull through. Now I just have to deal with a bird. He ate 5 fish while I was on vacation. Then I shot him with a pellet gun and he went away for 2 weeks. I thought the problem was solved. Then 2 days age he got another fish. I netted the pond and got up at 6am yesterday to try to get him again with the pellet gun but he didn't come over.