A friend we know who has a medium-sized pond of around 400 gallons balks at making water changes. His wife claims the changes are stressful on the fish. He claims his water looks fine. Of course, he can’t understand why he lost eight fish last year or why he’s medicating another half dozen in an aquarium in the house right now. But we understand. His water is high in ammonia, nitrites, and nitrates.
And why wouldn’t it be?
Think of a pond as something similar to the Middle East's Dead Sea. In most natural bodies of water, old water flows out and new water flows in, continually flushing the pond with uncontaminated, oxygenated, healthy water.
In the Dead Sea, new water comes in whenever it rains, but the old water never flows out. The sea loses water through evaporation, leaving behind all of the salts, minerals, and chemicals in increasingly higher concentrations. Over the years, that concentration has resulted in a body of water in which virtually nothing can survive.
Unless you make frequent water changes to your own “Dead Sea,” you’re doing the same thing to your pond that nature is doing to that land-locked lake. Why on earth would you ever expect anything to be able to live in that kind of environment?
How do you know when it is time to make a complete water change? One word: Spring. If you want to make sure, test your pond's water for nitrates. If the test shows more than 40 ppm (parts per million), it's time. I know that doesn’t sound like much, but remember that in nature, nitrate levels in water rarely exceed 1 ppm! Assuming you have no measurable quantities of nitrites or ammonia in your water (if you do, make a water change immediately), a high nitrate level of 40 to 60 ppm is a good indicator of the need for a drastic water change. If your biological filter is working properly, it will rid your pond of ammonia and nitrites, but the nitrates stay behind, gradually building up to potentially toxic levels. Get my drift?
On the flip side, if you have 20 to 40 ppm of nitrates and no measurable amounts of ammonia and nitrites in the water, you can rest assured that your biological filter is working properly. Now all you need to do is give it a little “nudge” to reduce the level of those nitrates.
Remember, though, that high nitrate levels accompanied by high ammonia and nitrite levels mean that your biological filter isn’t keeping up with the amount of ammonia being produced—ammonia that is converted into nitrites and, ultimately, nitrates.
If you have a large number of plants in your pond, they should be able to absorb the nitrates and convert them into oxygen--theoretically. But, even though we have plants galore in our main pond, they’re nowhere near enough to do the trick. We still get nitrate readings regularly hovering in the 20 to 40-ppm range; so, we still make regular partial water changes. And spring is the perfect time to do so, to get the year off to a running start.
Just remember that topping off your pond as the water evaporates does not qualify as a partial water change, since the evaporating water leaves behind the concentrated nitrates and other chemicals. In order to reduce the percentage of nitrates in your water, you must remove some of the existing water (and the nitrates, along with it) and replace it with fresh water.
What’s the best way to remove water from your pond? That depends upon your individual situation. We don’t have a drain in any of our ponds; so, we use a garden hose. We place the hose beneath the water’s surface, turn on the spigot, and, once the water begins running into the pond, turn it off again. We disconnect the hose from the spigot, and out comes the water via suction.
If you have smaller fish in your pond, make sure before using this method that you tape some netting to the end of the hose to keep those particularly nosy fish from getting sucked up and deposited on your begonias!
Once we’ve drained approximately 25 percent from the pond, (we put the drained water on our plants—they love nitrates, which are an integral part of commercial fertilizer), we hook the hose back up to the spigot and reverse the process. Just make sure to run the new water into the pond slowly. At this point, it’s a good idea to add some Amquel to neutralize any chlorine, chloramines, and ammonia in the new water to help protect your delicate plants and fish.