3 year old large pond, fish gulping for air...

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I apologize for not having any water quality data - I have several test kits on order from Amazon, but until they arrive (this Friday) I'm flying in the dark. Since the fish are showing signs of stress, and 6 have died within the last 24 hours, I figured I should post now before having concrete data.

The backstory:

The pond was installed about 3 years ago with the primary function of being a water reservoir for our property for fire protection. Little thought was given to make it a habitat for fish or other living creatures. The pond is approximately 75' x 50', with the deepest point about 4' down, average probably around 3'. Thus the total volume somewhere around 80-100k gallons. There is no liner. No filtration. The only source of water is gutter runoff from the house via 4" lines.

Shortly after the pond was filled (with primarily rain water and local stream transfers), we added 10 koi and 5 goldfish. The water was so turbid/murky, that we never saw the fish after they were put in. We added a Pawfly 8-Inch Diameter Large Air Stone with an 800GPH air pump to the middle of the pond, as well as a 2700GPH fountain.

About 6 months later, 8 ducks were added to the pond. They thrived, ultimately ending up with 11. For the next 2 years, we would only rarely see a fish as it broke the surface of the murky water. They were big - 20" or larger - so we assumed all was well.

The pond is located in middle-TN, where the air temperatures recently dropped into the upper 40s and stayed below 60 for the last several days. That is unseasonably cool.

Current story:

After recognizing the damage that the ducks were creating to the berm of the pond wall with their incessant burrowing, we realized that the ducks had to be rehomed, or we would lose the pond entirely due to a failed berm. Two days ago, the ducks were all re-homed.

The very next day, we noticed HUNDREDS of Koi and goldfish swimming at the surface gulping for air. We'd never seen this before, and were left scratching our heads as to whether the removal of the ducks caused this, or if it was just some odd coincidence. The surface of the water had a light green film that looked very much like excess tree pollen.

For the entire time since the fish were added to the pond, we have never seen a dead fish. Not one. The water as been murky since day one. With the duck feces the water only became more brown. So we had no clue how successful the fish had been populating the pond.

The 6 fish that have died in the last 24 hours were +20" (x2), 10" (x2), and 5" (x2). They were all very slimy. I could not see any obvious injuries, and since I was not familiar with their patterns, I'm not sure if what I was seeing was missing scales, or just unique markings.

There are at least a dozen +20" Koi swimming/drifting along the edges, and hundreds of smaller fish huddled all along the banks.

Attempted:

Thinking the gasping was due to lack of O2, we started pumping water from the pond, through the air utilizing several additional pumps (950GPH on several sprinkler heads and a 200GPM trash pump spraying across the pond with a fire hose nozzle). This eliminated the light green surface film (again, suspected to be pollen).

I also took a 33 gallon trash can packed it with pure cotton filler and non-treated foam. I'm running water through the trash can (with the 200gpm trash pump set at idle) and back into the pond to try and mechanically scrub some of the solid material from the water. Some of the fish are crowded around the return from the "filter".

The hundreds of fish at the edges continue to stay there - though they will disperse if approached.

The water surface now seems like it has a thin layer of slime/bubbles, but when picking it up by hand, it doesn't have any viscosity to it.


Request for help

At this point, I'm just waiting to get the test kits to get a better picture of the water quality. But given the story, what are your initial thoughts? What can I do to help alleviate the stress in the interim?

Doing very abbreviated research, my thoughts are to create a bio-media filter using lava rock in a 275 gallon IBC tote, preceded by another 275 gallon IBC tote filled with sponge/brush material as a bulk scrubber.

Please be gentle in your critique of my rather abysmal handling of fish. Keep in mind that the design and intent of pond never took into account supporting fish. The mistake was introducing them before learning how to take care of them. And of that, I am guilty as charged.
 
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Hi from Oak Ridge. Sorry to hear your fish are distressed, sounds like your trying some sensible things but without having test results you are limited. Glad to hear you've not tried chemical remedies until you get evidence to support it - that often complicates things.
Many more qualified than myself will step in to advise you, I'm just here to encourage you to hang in there until they have a chance to respond.
Photos are always helpful if you have any.
 
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Since the big fish are dying first, oxygen deprivation makes sense - but why? That's a large body of water. Could it be that something toxic got into the pond? Runoff or spray from a surrounding farm maybe? (Removing the ducks is likely just a coincidence. )
 
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Lost number 7 today. Does this look like an obvious illness?
 

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And that clear slimy looking film last night turned green this am....
 

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There is a slime covering their gills, and when I remove it it's bloody.

What a helpless feeling.
 

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Sorry to hear about your issues. Sure does sound like an excessive nutrient /dissolved oxygen issue. Blue green algae can also be a sign of this. Looks like you are doing everything possible in the interim. This article has some similarities to your issue and shows even the experts can miss some of the issues:

You mention a cold spell, what is the water temp of your pond?
 

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Sorry for all this happening to your fish. Hope someone here can help and hope you get the test kit soon.
 
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I agree that water test results will be very helpful.

Of note is concern for blue green algae as it is dangerous to humans and animals. Is there a way you can find out what type of algae is on your pond's surface?
 
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Any heavy rains lately, or neighbors/workers spraying pesticides nearby? So sorry, and please don’t blame yourself too much. Your health department or agriculture office might be able to have the algae identified for you.
 

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Sorry to hear about your issues. Sure does sound like an excessive nutrient /dissolved oxygen issue. Blue green algae can also be a sign of this. Looks like you are doing everything possible in the interim. This article has some similarities to your issue and shows even the experts can miss some of the issues:

You mention a cold spell, what is the water temp of your pond?


I don't have a thermometer in the water, but if I had to guess, I'd say it's about 75°. The air temp dropped unseasonably cold for a couple days leading up to this film. It's not the first time I've seen it. It's never gotten any worse than in the photos. It sits on the surface, nothing below. If I hit with water from a hose it dissipates quite easily.
 
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