What is tannin? Everything you need to know about pond tannin
Tannin is an organic, carbon-based substance that causes pond water to appear brown or yellow in color. The substance is a natural occurring byproduct of decomposing organic matter that enters your pond water, and the amount of tannin is directly related to the amount of debris present. During decomposition when beneficial pond bacteria begins breaking down debris, tannin is released into the water which eventually builds up and causes problems with clarity. Anything organic can release tannin, but in ponds the most common causes are leaves, soil, grass, and fish waste.
Tannin usually comes in the form of fumic acid or humic acid, and can slowly contribute to acidity (decreasing pH) of pond water over time. This and the reduction in water clarity makes tannin undesirable for most ponds, with it generally being removed to maintain clearer water.
Is tannin bad for your pond?
In low quantities, tannin is mostly an aesthetic concern, making water slightly less clear and giving the pond a tea-like color. Pond owners with low or moderate levels of tannins usually choose to treat the water to obtain better clarity, especially if you have goldfish or koi. Since mechanical and biological filter media cannot remove tannin by itself, tannin can slowly build up to higher levels were it can soon become more of a concern.
Tannin in larger volumes will drastically reduce water clarity, making it very brown or yellow in appearance. The problem with tannin is it always comes from decomposing organic matter, and when pond bacteria works to break down this waste, oxygen is depleted during the process.
The lower levels of oxygen, combined with heavy tannin-laden waters, can cause real problems for your pond fish. In this environment of lower oxygen, tannins begin to contribute to the problem of acid water, slowly lowering the pH over time. If the pH of your water drops too far, fish will soon become sick and can quickly die. The pond’s nitrogen cycle will also be negatively affected, with bacteria working less efficiently as ammonia and nitrites slowly build to harmful levels.
In most situations, ponds will never reach a volume of tannin that will cause these kind problems, but it’s often better to treat a pond with rising tannin levels just in case. If you want a clear pond especially, the less tannin in your water, the better your water clarity!
How do you measure tannin?
Measuring tannin levels in a pond is not an exact science, and is usually determined from a simple “eyeball test.” Visually checking the pond water in a glass and comparing each day to see if there are any color changes occurring is typically the easiest method. If the yellow tinge is becoming more pronounced, a treatment is usually recommended. Most pond owners will choose to treat their tannin problem as soon as it appears, as clear water is always a very desirable feature for garden ponds. Alternatively, if after a few hours the color settles to the bottom of the glass with the rest of the water becoming clear, the problem was sedimentation rather than tannins.
When to treat pond tannin is up to you! If you want maximum water clarity, we recommend an initial treatment to remove the bulk of the color, and then a maintenance routine to prevent it from coming back. Garden ponds with only a slight yellow tinge do not necessarily need to be treated unless you feel the tannin level will get worse in time, or if perfectly clear pond water is important to you.
Since tannin is an organic pollutant, and it has no benefits to pond water, and removing as much as possible won’t adversely effect your pond’s health. In terms of tannin concentrations, see the information below which shows approximate tannin in parts per million (ppm) and the corresponding water color. To note, anything above 2.0 ppm (darker tinge of yellow) we would recommend treating, especially if you have fish!
|Tannin in Parts Per Million (PPM)||Water Color|
|0 – 0.5|
0.5 – 2.0
2.0 – 3.0
|Light tinge of yellow in pond|
Darker tinge of yellow in pond
Light tea color in pond
Darkening tea color in pond
Removing Tannins from Pond Water
Method 1: Using Polywool Filter Media
One of the easiest ways to remove tannin from water is with a highly absorbent and fine filter media material called polywool. This material will be able to directly absorb tannin, as well as catch finer organic debris which may be contributing to the overall problem. Most mechanical filter media isn’t fine enough to catch such small particles, so polywool is used for maximum filtration on top of normal media.
It can be added directly to your filter box, but you will need to monitor pressure buildup carefully afterwards. Due to how fine the material is, it can greatly reduce water flow and can slowly build pressure inside of your filtration system. If you’re having problems with pressure buildup, polywool can instead be added directly under the filter outtake hose, under a waterfall, or even a fountain. A container or basket with holes can be fitted with the polywool and water passed through it to catch tannin and debris. The material will need to be changed once it becomes clogged until desired water clarity is achieved. This could be every few days, or once a week, depending on debris and tannin volumes.
It’s best to start with a thickness of around 12-15mm, and then slowly increase the thickness as as water clarity improves. Thin media can be folded and doubled up, or a thicker product can be purchased up to a maximum of around 50mm.
Below we have recommended some high quality, chemical inert polywool media designed for filtration in ponds and aquariums. These should provide good tannin removal, but we would also recommend combining this method with method 2 below for maximum water clarity and pond benefits.
Method 2: Using Activated Carbon Treatment
Another method of removing organic pollutants, such as tannin, from pond water is by using high quality activated carbon. Activated carbon is a great way to remove all kinds of harsh pollutants that your mechanical and biological filter media cannot remove by itself. Chemicals such as pesticides, chlorine, perfumes, and tannins can all be effectively removed by adding activated carbon to your pond’s filter system.
Activated carbon can be combined with polywool media for the best results, and is usually placed within a mesh filter bag inside your filter box. As water passes through the mesh bag, chemicals and tannins that touch the surface of the carbon are neutralized. The neutralized chemicals stick to the outer surface of the carbon, which means the activated carbon will need to be frequently replaced until all tannin is removed. The best activated carbon will have a very large surface area for chemical neutralization to take place, allowing faster and more efficient chemical removal.
Below we have listed our favorite activated carbon products for removing tannins and other organic pollutants from ponds. These can be added for water color removal until clear water is achieved, and then added every few months as a maintenance dose to prevent pollutants building up again. For more information on the benefits of activated carbon, check our full guide here.
Method 3: Water Change & Treatment
If the combination of polywool media and activated carbon are not removing color fast enough, or if you are already considering a pond clean up, performing a water change will help reduce tannin levels in water. This is not something we recommend over filter media or activated carbon, as water changes will reduce beneficial bacteria populations and introduce fresh chlorine into the pond system, which is present as residue in mains water. A water change will certainly help improve water clarity, but we always recommend treating the water with a dechlorinator afterwards to remove any residue chlorine which can harm fish and kill pond bacteria.
Dechlorinators are safe for pond fish and plants, and are a very effective way to neutralize tap water. If you’re considering water changes to remove tannin and improve clearness, we recommend a dechlorinator for best results; some of which we have listed below for convenience.
Preventing Tannin Problems in the Future
1) Install a pond net or skimmer system
Since most problems with tannin will arise from organic debris that falls into your pond and eventually decomposes, investing in a high quality pond net or cover is an ideal preventative solution. Netting will stop all leaves from entering your pond, which are a major contributing factor to tannin, and also help reduce sludge buildup overall. The less organic debris that can become waterlogged and sink to the bottom, the less muck and waste you will accumulate. Having a quality netting will also make cleaning your filter box easier, and extend the life of your pond pump as it will not become clogged as easily due to free-swimming debris.
Most pond nets are very cheap and durable, as well as being discreet and easy to install. If you have fish, they’ll also give them more protection from predators! For a list of our favorite pond netting solutions, check our guide here for the best netting and covers for ponds.
An alternative method of removing floating debris that falls into your pond is by using a pond skimmer, which automatically filters out surface debris with water flow. Although a bit more expensive compared to a pond net, they’re easier to clean and require very little maintenance. They also have the benefit of being able to remove all kinds of debris, even smaller debris that falls through a pond netting cover. For more information on pond skimmer systems, check our guide here.
2) Fix or replace broken pond liner
Color that is leaking into your pond through sediment (soil) is often caused by a tear in your liner or an improperly secured bank. Treating a pond to remove tannins caused by sediment deposit will not help much if soil continues to seep into the water. A tear in your liner can be repaired with a liner patch kit, or with special pond liner joining tape. Liner which has been fitted incorrectly at the banks would need to be re-secured above the water line, so pond water is not in contact with surrounding sediment. If there is not enough pond liner present, you can purchase more liner and simply attach it directly using pond liner joining tape. Our guide here will walk you through how to repair a leaking pond liner.
3) Regularly clean bottom muck
If you have a lot of pond sludge (silt) build up, this will constantly be leaking tannin and color into your water as it decomposes. Pond sludge in large doses can also become very bad for your pond, as it reduces dissolved oxygen and promotes algae growth. It can also leave a nasty odor around your surface water as the volume of sludge increases. The best way to remove pond muck is with a natural sludge eating bacteria product or with a pond vacuum cleaner. Both are effective at reducing sludge levels, with the vacuum being more ideal for larger ponds or fish ponds where sludge levels are usually best kept at a minimum.
4) Use activated carbon in your filter
Activated carbon is great at removing tannin and other organic pollutants, and is also very effective when used as a maintenance dose to prevent a return of buildup. Activated carbon has a range of benefits, not just restricted to color removal, and is a great product to add to your filter system. A dose of activated carbon should last 3-5 months for ponds with low tannin levels, so would only need to be replaced 2-3 times a year when used for maintenance. Check here for more information on activated carbon as well as our recommended brand picks.
17 thoughts on “How to Remove Tannins in Pond Water (Fixes & Prevention)”
I have a rather large backyard pond, for the last two years it is dark brown, it does not have a filter ration system as it is too big of a pond. I believe there has been a lot of corroding leaves in it from the past two years. How can I treat the pond? We would love to have its original color back.
How big is this pond exactly? Without filter media to help collect debris, your only real options would be DIY removal with a water vacuum, activated carbon treatments, removing sources of tannin (close-by foliage, trees, grasses), and possibly tannin-filters designed for house-hold use.
So long as your pond isn’t the size of a lake, I think simply cleaning the bottom muck with a water vacuum and reducing the sources of tannin could make a big difference in the long-run!
I too have a large pond…a little over 1/4 acre that is 12’ deep at its deepest point. The pond is fed by a natural creek and underwater springs. It almost always stays full even in the hottest times of the summer.
My pond water is also brown. I’ve been told that it is due to red iron algae. I do have trees at the mouth of the pond, some oaks, pines, and a hickory. But for the most part, the pond is open.
I lost my very large grass carp last year during a flood where he went onto the grassy dam while the water was cresting, when it receded the carp did not make it back into the water. Since then, the natural growth of weeds and the such on the bottom and sides of the pond have taken off.
The pond is stocked with bass. Sadly the bass have overtaken EVERYTHING and now I can’t put any other type of fish in the pond as the bass are so aggressive (and I guess hungry…I’m unable to find a pelleted food that they will eat) that NOTHING survives for very long after I put it in the pond.
So I have a multitude of problems…
The color of my pond is brown and unattractive.
My grass carp died and in order to get another one, I’m going to have to find a source for one as large or larger than my bass who average 8” long.
My bass make sticking the pond nearly impossible. I’d love suggestions short of killing all the bass, on how I might be able to get a healthy balance back in the pond. The pond was once stocked with catfish and several types of ‘bream’ type of fish (shellcrackers and another type), as well as minnows. Sadly with us not living near the pond ‘locals’ took advantage of the well stocked pond and now it is a mess.
Hi Kathy. First I want to say I don’t like using chemicals to treat ponds/lakes because they are temporary solutions and usually become very expensive because you have to continually treat the pond.
I would say that most of your problems are due to an overpopulation of fish and it sound like the bass are the main culprits. Too many fish will pollute the pond beyond its ability to naturally keep itself “balanced”.
Bass are predators and very aggressive. Most any type of fish are food for them. I think that keeping them in check is going to be your biggest problem. Finding what I call “maintenance fish” such as your carp that are big enough to survive with the bass is the second problem.
My first suggestions would be to remove some of the bass, probably a good majority of them. This will lessen the amount of waste they produce and will also give any new stocks a better chance of survival. The easiest and cheapest way I know of is by fishing for them or let others fish for them making sure that they take what they catch. When it starts to become more difficult to catch them then cut back on the fishing but do not stop as bass can quickly reproduce and you will be back to square one. I don’t think introducing another predator fish to control the bass would be a good idea. I think it would just compound your problems.
My second suggestion is to install some type of aeration system. This will help with the overall health of your pond by raising the oxygen levels. It could be that your stream feeding the pond would be large enough that once you reduce the bass population you won’t need mechanical aeration, but by adding a mechanical aerator your pond will be able to support a larger population of fish. There are many types of plants that you can add that will help with aeration, but you have to be careful with them. Many are very invasive and will quickly take over.
My third suggestion is for stocking your pond. It can be very difficult to find a supplier of larger fish to stock with and as you know putting in fingerlings is just feeding the bass. I suggest calling your local fish and wildlife office or the conservation office and see if they can point you to a supplier, or if they have a program that has adult fish that private pond/lake owners can buy. They may even be willing to send a biologist to look at your pond to give you more specific ideas on restoring it.
Unfortunately bringing your pond back into balance will take a several years and you will not see results for awhile. Finding the balance between types of fish, the total amount of fish,and plants can be very challenging. Good luck and remember that perseverance is your best friend when dealing with these issues.
I’ve just built a new pond in my garden and it’s gone very dark colour after we had some rain.
The only debris is blossom from a nearby Ash, birch and cherry blossom tree.
Will this clear up on its own? We don’t have any fish in our pond but lots of newts and frogs.
It’s normal for water to become dark and murky after a rain, especially since it’s a new pond and probably wasn’t fully settled to begin with. It should clear up within a few days, but if it doesn’t please leave another comment!
Thanks for all the above advice. I have a situation somewhat like Kathy. I have a 3/4 acre pond, 15’ at its deepest and very steep banks. We have some foliage around it but mostly small shrubs. We have resident ducks and local frogs. I have also stocked it with Rainbow trout, not many but enough for the kids to catch. The water since we moved to the property has always been dark tannin. I have cleared some shrubs and other culprits (huge maple upstream) but am wondering what I can do. I have an aerator and it’s been going 24/7 for 2 years. Climate is temperate as we live on Vancouver Island. Short of draining the pond and starting from scratch I really have no idea what I can try? Any suggestions are greatly appreciated! Thanks!!!
Thanks for reading!
I would suggest trying the first two approaches listed in the article (using polywool to capture the tiny tannin particles and any other floating particulate debris that may discolor the water, and if that doesn’t work trying to use activated carbon, or vice-versa. These can also be used in tandem). If neither of those options work, then draining your pond is your next best bet. If you do perform a complete water change, you’ll of course need to dechlorinate it, and add back in some beneficial bacteria to help out the fish. Keeping an activated carbon filter in your filter/aerator should help, as well!
Best of luck, and let us know if any of the above methods help!
Thanks for the reply Beckie.
I guess I’m just wondering about the costs. I mean my pond has 2+million gallons of water in it. The aerator is 50ft of weighted tubing so I’m not sure how I could add charcoal to it either. Apologies if I wasn’t clear on the size of the pond. Or if I’m missing something else and polywool really could work on a pond that large.
For a pond of your size and depth, you’d likely need to look into larger solutions designed for lakes. One potential solution would be with an organic scavenger system, which works similarly to activated carbon (some actually use it, too), but on a much larger scale. Essentially, these systems contain a strong base anion resin with a very porous structure which works to capture the organic content in the water. I’m not sure how widespread they are in Canada, but it may be worth enquiring with some local water treatment and/or water tech companies for advice. Many of these systems are intended for the medical or manufacturing industries but can be modified for use with lakes and ponds, as the core mechanism remains essentially the same.
Here is an example of a company offering these systems:
And here is some further information on how they work:
A cheaper alternative, and more ‘DIY’ solution, would be to create your own activated carbon filter! For example, studies have shown that adding a layer of activated carbon to regular sand filters have been massively effective at reducing tannin and organic pollutants in lakes: https://link.springer.com/article/10.1007/BF03039965
A regular high-capacity sand filter designed for pools or large ponds could work well, such as this kind: https://amzn.to/2zH68cB
But you could also contact some local companies who offer these filters for pools and ponds and explain your situation. So long as you can provide the activated carbon media a steady stream of water, and assuming the on-going tannin production of the pond doesn’t outweigh the carbon’s capacity to remove it, this kind of system should work to slowly reduce tannin.
I hope this helps and give you some ideas!
We recently bought a house that came with a very small pond and did whatever research we could to revive this pond to make it a habitat for our new friends.
We have a smaller size pond (20′ X 14′ X 1.6 deep) in our backyard which is out in the open where the sun hits it throughout the entire day. No trees surrounding the pond but our next door neighbor has very tall pine and sugar maple trees which are about 50 feet from the pond. We have the following in our pond which consist of waterfall with assorted filters, skimmer and aeration pump and a UV light. Plus, 15% lilly pads, 5% bog grass, a 5 foot bridge that provides some shade and a rock cave underwater for the 6 small Koi’s and 4 small Goldfishes. We have notice with the constant falling of pine needles and maple leaves each day (August) its been a headache to maintain constantly. The pond water is very clear but the rocks and gravel are turning a dark color brown. Algae is constantly blooming due to open sun exposure and constant raining. Each week (Thursday) been testing the Pond with a Master kit PH 7.0-8.0 , Ammonia 0, Nitrite 0, and the Phosphate 0. Plus, each week (Saturday’s) do a 10% -15% water change. Each morning skim the pond surface for fallen leaves or anything stuck in skimmer catchment. Recently bought a 1/8″ pond netting due to neighboring trees. We have no catchment for extra water so only using groundwater from our hose to refill pond with Chlorine remover, from time to time we add Pond salt. Someone mentioned to us about the use of Active Carbon?
Please advise and thanks for any feed backs greatly appreciated
We have a small pond (1/3 acre 6′ deep) that over the years has a build up of sludge or muck at the bottom due to grass clippings, leaves, algae decomposition, etc. It is spring fed with no inlet or outlet of water. There is also no power source to the pond. What do you recommend to remove the muck that may help reduce algae growth in the future.
Hi, I have a new container pond since the spring with a few plants and 2 goldfish. This week I have noticed the water has become duller. The weather is a little cooler and the 2 fish are much more active. But 1 of them has turned black around the middle. Is he sick??
The pond is quite small- an old tin bath. And sits near a very young cherry tree
Thanks for the post. Now I can apply them to remove tannin from water by myself easily.
I used activated charcoal in my tank and it really worked.
We’re glad the article was helpful to you! Thanks for reading.
Hi Beckie, this is excellent info you are sharing here. Our pond is about a half acre, 10’ deep with gently sloping banks. It is lined, with 6” of sandy gravel covering the liner. It is fed with two 5gpm solar slow pumps bringing water from a cold spring. I just reinstalled an aerator after a few years without one. It seems to have accelerated the tannins and the water now is very brown. There are too many maples, cherries, and oaks along a long side, too many to remove. I have a very healthy population of numerous generations of healthy koi and goldfish. No other fish at this point. So, no filtration but an outlet that feeds a small lotus pond. Anything I can do to help clarify this pond? I’ve been researching barley extract, but I’m not sure it would help with tannins. Any suggestions? And, thanks!