Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Where did my fish go? DO problem?

Background: My pond is complete after about three years of construction. It is watershed fed and is now 1.6 acres and about 15' deep. The goal of the pond is to have a good YP and SMB fishery, and hopefully BT in the future. It is well established with FHM, GSH, Eastern Silvery Minnows, crayfish and PK shrimp. There is very little vegetation as of yet. The water is tannin stained from Eastern Hemlock and looks like diluted ice tea (clear but brown).

I have stocked a total of about 200 6-7" YP and 25 5" SMB between Fall of 2024 and Fall 2025 and have no proof of life after fishing and setting minnow traps. The YP should have pulled off a spawn in Spring 2025. I was hoping that I could catch their fry in minnow traps baited with dog food. I caught all of my forage species but no YP or SMB. The SMB probably haven't pulled off a spawn yet, but if they're in there they should be large enough to this Spring.

I have fished open water with live and artificial bait and done the same through the ice with no signs of life beyond the forage. I have found a total of maybe a dozen dead perch (mostly on the bottom in 2-3' depths) and no dead SMB. I'm an avid trapper and have seen no signs of otters. GBH visit occasionally but they fish in less than 1' deep (I suspect the tannin staining limits their visibility). The pond is the center piece of the property and is visible from the back windows of the house, so I'm assured there are no trespassers.

I have not installed aerators yet but ran conduit underground from the house to the pond edge in the event that I need power there in the future. I don't object to installing an aerator, but the pond is used for a closed loop geothermal heating a cooling system and I'm not clear on how destratification of the water column would impact the efficiency of the geothermal.

Recent posts by essup and others regarding DO under the ice made me consider low DO as my culprit so I tested it tonight using the CHEMetrics kit and used a digital meat thermometer from my kitchen. There is currently 22" of ice with about 16" of snow covering, although I have kept about 10% of it cleared of snow to allow some light penetration. Here are my results:
2' 36.1F 8ppm
4' 37.6F 4ppm
6' 37.2F 1ppm
These were all taken just after sunset after a clear and sunny day. Depth is relative to the top of the ice, not the bottom of the ice so 2' deep is actually a couple inches under the ice. I suspect that my ice fishing has been mostly too deep, so that is likely why I haven't caught any through the ice this winter. I'll try shallower.

I read a study that suggested a lower DO limit of 2-3PPM for YP, however it suggested they can tolerate lower concentrations temporarily without much negative effect. It also suggested that "in general, the first response of fishes to severe hypoxia is avoidance." That gives me a little reassurance that they should be able to survive my current DO levels, but would likely not be at depths below 4' for extended periods. Here is the link for those who are interested: https://www.sciencedirect.com/science/article/abs/pii/S1095643317300879

Based on what I have read, DO levels of 5-6 or greater are ideal for SMB. Given that, my results above worry me that they may not have survived.

The reason for my post (and my sleep deprivation) is trying to figure out where my fish went. Are they dead at the bottom feeding my crayfish, or are they avoiding my efforts to find them? As I said before, I have a very robust forage base and low density stocking numbers. I expected catching them would be a little bit of a challenge, but I have completely struck out.

My plans moving forward are to fish at shallower depths until ice out, then deploy fish traps. So far all I've used are Gee style minnow traps baited with dog food hoping to catch fry. I'd love to hear the advice of others here on how to survey the pond. Unfortunately there aren't pond management companies here in New England like there are in the south, so shocking isn't a realistic option.

Also, what are recommendations on aeration given my DO numbers today? Is it required? Should I expect a complete kill of my YP and SMB has happened based on my DO numbers? How might aeration effect the geothermal system? I'm willing to accept lower geothermal efficiency for a healthy pond ecosystem.

Airration would help with the oxygen level and help you use the depth of the pond. You mentioned the water quality with the near by trees. What is the ph level? My guess is low. As far as the geo system,talk with the installer. Are the lines just laying on the bottom or are the buried below?
Side note i just switched from geo to nat gas. My electric bills were crazy. Not the best system for cold climates. Its crazy how 70 degrees feels so much warmer now. Kinda hard to explain, you would think 70° would feel the same with either system.

If your readings are accurate then I don't think DO got many fish. Fish move to where O2 is present so if you had 5-6 ppm DO the fish will not have died from that. Possibly something else or likely they are still there.

Re: Geo systems. Unless you have a whole house humidifier, the lower humidity in the house during the winter makes a HUGE difference in the "feels like" temp. I can run my pellet stove and keep the house at 69°F - 70°F and the house feels cold with relative humidity levels in the mid 20% range. I can turn on the forced air propane fueled furnace to keep the house at the same temp along with a whole house humidifier that is added onto the forced air furnace. The house feels comfortable at 70°F with a long sleeve t-shirt on.

The other house has a wood burning insert and can heat the house to whatever temp I want. As a test one winter I had it 100°F over ambient temp (-20°F outside). I can run 3 ultrasonic humidifiers in that house, putting 6 gallons of water into the air and I cannot get the humidity over 20% there. The house also has a natural gas forced air furnace, but there is no whole house humidifier installed on it, so the house needs to be 74°F-75°F to feel the same comfort level as 70°F in this house. That house is built on a crawlspace, and the floor is not insulated - so there is more outside air moving in and out of the house.

A customer that is local here has an open loop geothermal system. Our ground water is 53°F - 54°F. the system dumps into his pond. His system needs propane back-up in the coldest part of the winter. He has a separate whole house humidifier built into the forced air A/C system that keeps the humidity in the house where it feels comfortable.

What is the Relative Humidity in your house this winter?

For the winter with your in-the-pond geothermal system, fresh water is the densest at 39°F. So you should be seeing 39°F water at the bottom of the pond. That 39°F water sinks to the bottom of the pond and water that is colder than that OR warmer than that will come to the surface. I am assuming that your temps are a wee bit lower due to the geothermal system sucking some heat energy out of the water. In my pond, since I have a groundwater pond and water moves through the pond as it moves through the ground, my deepest pond water temps usually are around 40°F., even with the aeration system running.

Since the winter aeration system is not designed to disrupt the lower denser, therefore, warmer water, it shouldn't have much effect on your geothermal system. A properly places winter aeration system might affect water temp down to 6'-8' because the diffuser should be placed at 1/4 to maybe 1/3 the total pond depth, close enough to the shore that anything that might go swimming can get to shore to get out. I would go talk with the geothermal people in regards to your water temp in the pond to see what a degree or two of change might mean to the geothermal system.

At what water depth are the coils placed in the pond? Can you take a temp reading within a foot of those coils? That might help you when you talk to the geothermal people.

I learned that using a fish finder while ice fishing made a HUGE difference in figuring out where the fish were. They don't have to bite to be seen. I can also see the zooplankton/copepods/daphnia on the screen. It shows up close to the pond bottom, but as the light levels diminish (at sunset) I can see it rise up off the bottom and move towards the surface of the pond (following the sunlight). A few weeks ago I caught crappie and bluegills 2' under the ice.

The only way you will know for sure about the YP and SMB is to fish for them when the water temp is in the mid to upper 60's once the ice is gone.

I agree with Ron in asking what the alkalinity of the pond is? A simple test strip should tell you that, and it might also tell you what the pH is in the pond too.

The tannins causing the "tea stain" color of your pond are probably now mostly in the form of humic and fulvic acids. These are very weak acids, and are NOT generally a problem just by themselves. However, these are chemically reactive molecules, so your pond chemistry may be a little more complex than the typical pond discussed on Pond Boss.

If these acids persist throughout the entire year then your pond might even be buffered to be in a low pH (4.0-5.0?) range for most of the annual cycle. I definitely agree with the good advice above to do some water testing. However, it may be difficult/expensive to raise your pH to the optimal level for your fish if your pond has some significant buffering (humic/fulvic system) capacity. If my speculation is even close, then you may need to manage your pond as a "lower pH" pond. That is way above my pay grade, but we do have some experts to help if that proves to be the case after your water testing and some remediation efforts.

The good news is that the tannins are not DIRECTLY affecting your dissolved oxygen levels. However, with ice cover AND dark stained water, you may have very low photosynthesis for oxygen creation during the winter months. Some aeration may be of great value. Do you have any neighbor buddies with fish ponds and the same local conditions? Their advice may be much more valuable than some yahoo in Kansas!

Finally, I do hope your initial fish stockers are still alive. Don't give up on them until you have fished extensively during warmer water temps.

Thank you for those who have added their input. I sincerely appreciate it. Here are a couple follow on points and responses to your questions.

I sent water samples to Texas A&M University for testing. Here are my results from a month ago, with results from April 2024 in parentheses, followed by the "normal" range.
Hardness ppm 55 (15) 50-150
Calcium ppm 15.6 (4.26) 15-45
Alkalinity ppm 17 (4) 50-150
pH 6.73 (6.22) 6.5-9
Salinity 0.04 (0.03) 0.5-3
Nitrite ppm 0.022 (0.01) <0.5
Total ammonia nitrogen 0.45 (0.47) <1.0
Unionized ammonia 0.001 (0) <0.25
Chlorides 20 (40) 50-100

Between the first test in () and the more recent test, I added 4,400 lbs of ag lime and 750 lbs of ag salt (non-iodized). I added less than the recommended amount of salt because that was all I could get from the local ag store at the time. The recommendations were 150-200 lbs/acre foot (about a ton for me). It looks like my efforts where worthwhile, but there is still some improvement to be made in the chemistry.

The geothermal is a closed loop system with coils that are buried under the frost line about 150' through my yard. They extend into the pond about 4' below the surface so they are safe from freezing. They naturally float so I weighted them down so they would sink. There is a coil of this plastic line that looks like a giant slinky, about 3-4' in diameter and about 10' long. This was weighted down with 250 pounds of ballast. It is in about 10' of water. I don't have a temperature of the surrounding water immediately around it, but I'll try go get it.

We're happy with the geo system so far and have had it running for a little more than a year. It is a new house with great windows, 2x6 walls and spray foam insulation throughout and the current indoor humidity is 38% without a humidifier. The geo furnace has a built in 220V electric heat back up that has never been used except during testing when it was installed. The house is as warm as we want it and costs about $300/yr to run when accounting for the solar panels on the roof that produce most of our energy needs.

I haven't tested the temp and DO at the bottom of the pond. I expect the DO is negligible. Where I took the measurements in the original post is about 10' deep but I could only sample up to 6' deep. That's from the top of the ice, not the bottom of the ice, so my 6' measurements were really 4' under the ice, since the ice is nearly 2' thick.

There is some flow through the pond even on the coldest days of the year. I haven't measured it but I would estimate that it's only about 10 GPM now. I have seen it running at 100+ GPM before and it will be again soon as the thaw starts.

I've tried a Vexilar flasher on the pond and didn't mark any fish. Given my DO readings, I was fishing too deep though. I've considered having someone with a side facing sonar come out and "survey" the pond to see if we can find anything. That may be my next move.

Regarding the tannins, my water looks a lot like other natural bodies of water near me including a very small pond connected to a stream about 1/4 mile from me that holds GSH and a naturally reproducing brook trout population. In fact, it is fed by the same watershed as my pond. I have noticed that this very small pond has a decent fish population during open water but I tried trapping minnows there last winter and got very very few. In open water it's easy to get a few dozen GSH overnight. I even caught a 6' BT that made it's way into a small Gee minnow trap.

Given that my pond is fairly new and therefore has very few aquatic plants, I expect I have very little O2 production (especially when most of the pond is under 16" of snow). I had some FA, however there are biblical numbers of crayfish in the pond so they seem to keep that in check. I intend to plant wild rice and pickerelweed this Spring for some emergent vegetation and fry refuge. Hopefully the phytoplankton and other microscopic plant life are producing some O2 through the ice.

Ponds are much less common in this part of the US than in others, so unfortunately there isn't such a thing as a pond management company I can call on for help. Thankfully I have the knowledge and input of each of you on here to help guide me and I'm sincerely grateful.

I saw a pond a couple miles from me on a satellite image and am thinking of dropping by the house next to it to see what there experiences have been.

Here are a few photos that might help.

[img]https://imgur.com/a/G8zDnUC[/img]
Here is a look at the geothermal coil pack.

[img]https://imgur.com/a/AeLtmt4[/img]
My very low tech lime application technique. It took awhile to get 4,400 lbs of lime dispersed when I could only take 200 lbs at a time in the little boat without sinking it.

[img]https://imgur.com/a/fotp6yL[/img]
My very low tech water sampling system. It's a 50mL syringe taped to a 6' piece of electrical conduit. I marked the conduit at 1' increments from 1-6'. There is a string attached to the plunger on the syringe. I send it down to the depth that I want to sample water from, pull the string about 3" and I'm collecting water from the depths rather than just at the surface. An O2 meter would likely be easier and more accurate, but for my purposes I think this will work for the CHEMetrics DO test kit.

[img]https://imgur.com/a/XIc8cuN[/img]
View of the house as the pond was filling.

Thanks for posting the water testing results.

I am glad to be very WRONG about the possible pH in your pond water!

I also like that your pond has some water flow throughout the year. I think that moving water tends to have more DO, all other things being equal.

However, that is a non-expert opinion, since I have not tested DO in numerous adjacent ponds like some of our experts have. I will note that the water in my creek has MUCH different phytoplankton blooms and FA when running rapidly compared to my ponds. When the water flow decreases to a bare trickle, then the water in the creek and in my ponds start to more closely align in appearance and ecology.