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Healthy Water, Healthy Fish

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What do chemical pollutants and sunlight have to do with ponds?  They both play a key role in the health of pond fish.

Fish are sensitive to chemical pollution.  Avoid using any chemicals not specifically labeled safe for fish anywhere near your pond.  That includes herbicides for your lawn, fertilizers for your flowerbeds, and insecticides around the perimeter of your house and patio.

Three other chemicals that can prove deadly to fish are ammonia, nitrites, and nitrates.  Ammonia is created from decomposing plants and fish waste and is highly toxic in large concentrations.  Beneficial bacteria can convert ammonia into less toxic nitrites, which other bacteria can convert into only mildly irritating nitrates.  It’s important to have these beneficial bacteria present in your pond to prevent the nitrite levels from skyrocketing.  Too many nitrites will prevent fishes’ gills from utilizing the oxygen in the water, silently suffocating them to death.

If your water tests high for any of these chemicals (simple home test kits are available), you should make an immediate major water change—draining at least 1/3 – 1/2 of the pond and replacing it with fresh water.  The fresh water, of course, doesn’t actually combat the nitrites or nitrates, but it does dilute their concentration to a more fish-friendly level.  You should also add some zeolyte clay and use a charcoal filter to further reduce the dangers.

Remember when adding water from the tap that most communities use chlorine or chloramines to kill off bacteria and other human-unfriendly critters.  Too much of either of these chemicals can also adversely affect your fish, resulting in weakened immune systems and occasionally even death.

Fortunately, unlike nitrites and nitrates, chlorine and chloramines can be neutralized simply and efficiently by adding inexpensive compounds, including commercially available regulators such as Amquel, to your pond.

Limited Sun for Healthier Fish!


Fish enjoy early morning and late afternoon sunlight.  They are cold-blooded animals, meaning that their internal temperatures adjust to match that of their surrounding environment.  That’s one of the reasons that fish, much like people, prefer to rest in the shade during the hottest part of  the day.  They require some sun, but they also need enough shade to escape its heat whenever necessary.

To provide shade for our ponds, we rely on existing trees, nearby fences, and a small homemade “bridge” that runs from the front wall of the pond to the back.  It’s built out of rough-cut cedar to resist rotting and covered with Spanish moss.  We planted the bridge with baby tears and several types of grasses to make it appear natural.  As a bonus, the plants’ roots hang down into the water, giving the fish something to nibble on while keeping the water oxygenated.

Other excellent sources of shade are floating plants, such as water hyacinths, water lettuce, parrot’s feather, and duckweed.  These plants sit on top of the water and block out the sun, providing a natural canopy for the fish below.  Water lilies can also be useful as shade generators, in addition to providing a profusion of colorful flowers all summer long.

Fish enjoy rooting around various floating and underwater plants.  Some of our favorites are cattails, hardy water lilies, water hyacinth, marsh marigold, and water lettuce.  The fish love to nose around them in search of food and sometimes nibble on the leaves, sort of like a fishy Caesar’s salad.  Plants are also useful in that they absorb nitrites for their own growth and give off life-sustaining oxygen in the process.  It’s a win-win situation.

But beware.  If you have koi, be prepared to replace plants often, as the fish are notorious grazers.  One medium-sized koi can denude a dozen or more water lilies over the course of a single growing season.  While goldfish can be mildly destructive on occasion, they are far less so than their Japanese cousins.

What Next?

One word of advice to small-pond owners: be especially vigilant.  Since small ponds contain relatively little water, their chemical makeup can change dramatically within a very short time.  Large ponds with more water, greater surface area, and a larger turnover rate can hold more chemicals without endangering your fish.

If you’re thinking of building a fish pond, consider these two opposing scenarios:


Best-Case Scenario
: You have a 500-gallon or larger pond stocked with 10 medium-sized goldfish and small koi.  The pond is equipped with a large-capacity pump and filter.  The pump moves the water through a hose 20 feet uphill to a spillway, where it dumps into a small holding pond filled with cattails before cascading over a second spillway and into a meandering stream lined with watercress, bull rush, and other living plants.  From there, the stream washes over a third spillway into a larger holding pond also filled with living plants, including water lilies and hyacinth.  Finally, the water spills over a fourth spillway and down another short planted streambed before emptying back into the main pond.

Advantage: You will nearly never have to worry about a sudden buildup of nitrites, nitrates, ammonia, chlorine, chloramines, or virtually any other chemical pollutants.

Worst-Case Scenario: You have a 30-gallon wine barrel with a small pump-and-fountain and six small goldfish.

Disadvantage: You will nearly always have to worry about a sudden buildup of naturally occurring chemical pollutants, and you’ll constantly have to monitor the condition of your water to keep your fish healthy.

Of these two scenarios, one pond isn’t necessarily better for you than the other; it’s just part of the game, something to be aware of.  In the end, isn’t that what being a responsible fish-pond owner, a responsible human being, is all about?  Watching, observing, learning, acting, reacting—being in tune with Nature so that you can be in tune with yourself.

Happy water gardening!

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