Tannins

Tannins are nothing but tea, which is made in many ponds by many different contributors. You don't have to have an Aquascape pond to have tannin troubles. Any pond with runoff or leaf litter in it will have tannin accumulations so we see that tannins are a "pond thing" not associated with any particular brand. Fortunately, there are ways to prevent it, and ways to control it.

Tannins come from any plant material (and even some foods) which is steeped in the pond water (even in the skimmer if infrequently emptied). Over time, the leaves, acorns, seeds, or other material will leach tannins or brown staining dyes from the organic material. This will contribute acidic brown colored stains to the water. Sometimes the effect is very subtle and is most easily diagnosed only when white fish descend to the bottom of the pond. When these lighter colored fish are on the bottom, you might notice that they're not "white" anymore, but actually a pale amber color.

In other cases, the pond is so steeped in tannins that you cannot see the fish in the depths. This is unacceptable.

The primary means of prevention of Tannins is via netting placed over the pond in several different configurations. Bird netting is cheap and easy to deploy. Some folks use a structured frame of PVC over their pond and bind the bird netting to that. Others use a net with a long handle to skim leaves every day. I am not the best, most diligent pond keeper in the world. So, I let the leaves fall into the pond. I tolerate the tannins while the leaf fall continues. As soon as leaf fall is "done" I simply drain the pond more than halfway, and send a high school kid into the pond with a net to dredge out the leaves and acorns. Then I refill the pond and if needed, I do a supplemental water change later. Fortunately, leaf fall is only once every year. It varies by month depending upon how far from the equator you are.

The BEST way to handle leaf fall and tannin prevention is via netting because it keeps leaves OUT of the pond entirely. Acorns get through most netting, however, and every rain that goes through the leaves ON the net will contribute some tannin tea, so no method is perfect.

Finally, activated carbon is a fine, mechanical way of removing tannins. If you deploy enough of a good quality carbon, say 1 gallon of highly purified carbon, per 1,000 US gallons of water and you make sure you can channel all the filters water to percolate THROUGH this carbon, (in the absence of remaining or additional leaves to replenish and overwhelm the carbon) you will enjoy a disappearance of the amber color within 1-2 weeks.

I recommend that you would net the pond at leaf fall and try to keep the netting free of excessive leaves so that rain doesn't bring tea through the net. Net out any acorns that enter the pond as soon as it's convenient. Clean the pond, or do a water change as needed to control really noticeable tannins and maintain your level of control with activated carbon.

How do Tannins hurt the fish?

I don't think they do "hurt" the fish, actually. HOWEVER, they are a form of water quality deterioration that causes the fish STRESS. This makes the fish more vulnerable to infections and parasitisms. So, tannins aren't a "good thing". Bear in mind that it's been my experience that if a fish has a skin lesion, (sore) it will not heal in tannin stained water. This would be good to remember.

But, doesn't tannin occur in the wild?

The answer is yes and no. Take the blackwater Okeefenokee Swamp in Florida, for example. Not alot of great fishing there. That's because fish cannot thrive in (not even live in) that tea. That's the effect of cypress stumps and cypress litter in the water for millennia. Only specialized strains of acid tolerant fish (Cheirodon axelrodii and Symphysodon discus are examples) will live in the black water of the South American Amazon basin. Normal fish just won't live at all. The fact is, in nature, most freshwater bodies of water are constantly replenished by vast amounts of rain water. In your pond, measured in mere gallons instead of acres-foot, you are Mother Nature and YOU are the "giver of new water" to dissolve and dilute natural and unnatural pollutants. Are you doing it?