Copper

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Copper

Many people are properly concerned about copper in pond heaters. Copper is very toxic to Koi and must be carefully considered.

The copper in many heaters is limited to about a 2 foot long pipe about an inch in diameter in the heat exchanger. It often is U-shaped and does have copper fins attached to its outside surface, but the water never sees the large surface area of the copper fins. Many Koi ponds use water from homes plumbed with copper pipe. The water in this pipe travels through copper pipe that is much longer than 2 feet, and the Koi survive fine.

How do we deal with copper toxicity:

Water changes

If there is copper in the pond water we need to be vigorous about water changes. See the section on "Water Changes".

Water chemistry

pH - lower than 7.2 will eat up the copper in the heat exchanger, and thereby raise the copper concentration in the pond. Using baking soda will buffer the pH closer to 8 to 8.5 and eliminate this problem.

Hardness - research has shown that harder water will reduce the copper toxicity to Koi by a factor of 20 times. Keeping your pond water hardness levels to the recommended levels will reduce the copper toxicity. Baking soda also increases the alkalinity hardness levels.

Salt water - salt water (3% salinity) corrodes (dissolves) copper faster than fresh water. Many ponds have 10% of the salt level of salt water, i.e., 0.3% salinity. The higher salinity means you must carefully control water changes, pH, and hardness.

There are other heat exchangers available than pure copper. One used for many salt water aquariums is a copper-nickel alloy. It is a good solution, but is more expensive than the standard copper heat exchanger.

Another choice is stainless steel. However, stainless steel is very expensive, and it is not available in all sizes of heaters. Stainless steel is also not nearly as good a heat conductor as copper in the heat exchanger. So instead of copper's 82% efficiency the stainless heater's efficiency drops to much lower levels. This means they are more expensive to operate.

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