Q: How does carbonate hardness affect my pond and fish?
Bob – Underhill, VT
A: Hard water, soft water – you’re probably familiar with these terms as they relate to the water flowing through your home’s plumbing. But the water in your pond or lake can be hard or soft, too, and it matters to your fish, particularly if you’re using algaecides or herbicides.
A Natural Buffer
The technical term for hard or soft water is “carbonate hardness” and, simply put, it refers to the amount of calcium and magnesium present in the water. The greater the water’s alkalizing mineral content, the harder the water is. Those microscopic minerals actually act as a buffer that offsets swings or dramatic changes in your pond or lake’s pH level caused by chemicals found in algaecides and herbicides.
The beneficiaries of the hard water’s buffering calcium and magnesium are your fish. Carbonate hardness in your pond or lake affects the sensitivity of certain fish—mainly trout, koi and goldfish—to the acidifying chemicals found in algaecides and herbicides. If you have high carbonate hardness, or hard water that contains more than 50 ppm of the minerals, the fish are less likely be affected compared to those fish in that are in soft water.
If you’re curious about your water’s carbonate hardness level, or you plan to use an algaecide or herbicide in your lake that requires hardness to be at about 50 ppm, test your water with a Carbonate Hardness Test Strip.
The strips are easy to use. Simply open the pouch and dip it into the water for three seconds, remove it from the water, wait 20 seconds for the water to mix with the solution in the pouch, and remove the strip. To see what your water’s carbonate hardness is, match the color on the strip to the color block on the package.
Remember to perform this test each time before you treat your pond with herbicides or algaecides as the levels of calcium and magnesium in the water may fluctuate.
Pond Talk: How often do you test your lake for carbonate hardness?