How to Test Chlorine in a Pond

Updated July 20, 2017

A backyard pond is relaxing, and many people like to add koi or goldfish to their ponds as an additional feature. But a pond is far from relaxing when all your fish die unexpectedly. One of the main causes of fish death in a pond is the presence of chlorine, often from the water used to fill the pond. Most municipal water is regularly treated with chlorine to help keep bacteria levels down, but chlorinated water is toxic to fish and, even at low levels, will cause their death. Testing your water for chlorine each time new water is added is the best way to determine if you need to add a de-chlorinator to keep your fish healthy.

Dip your test strip in the pond, or collect pond water in your vial, depending on your particular test, according to the manufacturer's instructions; some test strips and vials should be swished or swirled and some should be held still.

Add reagents according to the instructions for your test if using a liquid test kit.

Keep the test strip in the water, or the water in the vial, for the length of time specified for your test kit.

Analyse the accompanying comparator, usually a printed colour card or incrementally coloured liquid, to find the closest colour match. This will tell you your pond's chlorine range.

Collect a water sample from your pond, measure it according to the manufacturer's instructions, and pour it into the test's collection tube.

Add the indicator liquid as specified in the instructions for your test.

Analyse the final colour produced by the indicator liquid to determine the level of chlorine in your pond.

Add the titrant liquid with the small dropper, one drop at a time, counting each drop until the liquid turns the colour specified by your test; the number of drops of titrant it takes to turn your water's colour gives an accurate reading of how concentrated the chlorine is in your pond.

Insert the instrument in a water sample from your pond, or in the pond water itself, according to the manufacturer's instructions.

Keep the instrument tip submerged for the specified amount of time for your device.

Determine the chlorine reading according to the instructions for your instrument.


Keep your hands and area clean before and during testing for more accurate results. Understand the directions for your test before beginning the testing process. Rinse your collection tubes in the pond before collecting your test water to remove any residue that may give you an inaccurate reading.


Use caution handling reagent and indicator liquids, as some can be harmful.

Things You'll Need

  • Chlorine test kit or electronic chlorine testing instrument
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About the Author

Cindy Crabtree's writing and editing career began in 2007. A former editor-in-chief of several magazines, she has contributed to "Boise Metropolitan Magazine," "Eagle Life Magazine" and "Meridian Magazine." Crabtree studied psychology at Boise State University and multimedia/Web design at the Art Institute of Phoenix.