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What is carbonate hardness and why does it matter? | Pond & Lake Q&A


What is carbonate hardness and why does it matter?

What is carbonate hardness and why does it matter?

Marlena – Richmond, MI

Carbonate hardness is a measure of the amount of calcium and magnesium present in water. As it turns out, these elements are vital to the health and well-being of certain fish – including trout, koi and goldfish – because of their ability to neutralize acids in water and stabilize healthy pH levels.

But why, you might logically ask, are acids a concern? You’ve just asked the sixty-four thousand dollar question. In the course of regular pond maintenance, it’s common to apply algaecides and herbicides. Often, those products contain chemicals that are acidic, and when they’re applied, they can cause pH fluctuations that certain fish are ill-equipped to handle. Thus, water that’s “hard” – or rich in calcium and magnesium – helps to minimize those fluctuations, protecting fish from harm. Other environmental factors, including runoff from fertilized lawns, can have a similar effect on pH, making it all the more important to ensure that your water maintains a safe level of carbonate hardness.

As a rule, algaecides and herbicides indicate a recommended level of carbonate hardness in pond water to ensure that their effects won’t harm fish. Low carbonate hardness is generally indicated when calcium and magnesium levels are below 50 parts per million (ppm). And fortunately, it’s easy to test your water to determine its carbonate hardness levels. With our Carbonate Hardness Test Strips, you can test your water prior to each application of algaecides and herbicides. If levels are above the range indicated on the product you’re planning to use, the pH of the water will be safe for fish even after application.

Pond Talk: Is water hardness a concern where your pond is located?

Carbonate Hardness Test Strips

One Response

  1. Carbonate hardness is actually a measure of the level of carbonate alkalinity present in the water in the form of carbonate (CO3–) and bicarbonate (HCO3-) ions. The measure of the level of calcium and magnesium (and other multivalent cations) in the water is referred to as “general hardness.”

    Typically, water with high carbonate hardness also measures high in calcium and magnesium due to underground rock that has dissolved in the water and served as a source of both the calcium/magnesium ions and the carbonate/bicarbonate ions in solution.

    However, it is the carbonate and bicarbonate ions that serve as the pH buffer in our ponds by combining with any acidic or basic substances that are introduced to the water supply and neutralizing their effect on the pH balance (i.e. preventing fluctuations in pH).

    Incidentally, when we use a test kit to measure carbonate hardness, we are actually measuring alkalinity levels. Alkalinity is the buffering capacity of the water defined as the ability to neutralize H+ ions. Carbonate alkalinity makes up most of the alkalinity in a typical pond. Other compounds that can contribute to alkalinity are phosphates, nitrates, silicates and hydroxyl (OH-) ions.

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