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How Water Hardness Affects Your Pond

Updated on May 12, 2015
Pond Water
Pond Water | Source

The measurement of your pond water’s divalent ions is known as water hardness. This is the condition wherein the water has magnesium carbonate and calcium. If you find yourself using water softeners at home, then your pond definitely has hard water. Hard water inhibits the growth of our pond fish and plankton. It can also decrease the potency of chemical plant treatments and algae treatments.

If you are fond of having fish in your pond, then you should always be aware of your pond water’s hardness. It is part of knowing proper water chemistry.

pH Levels and Water Hardness

Hard water usually has high pH. Soft water has low pH.

Take note that water hardness is related to pH. You should always check your pond’s water hardness because certain species of fish survive and thrive at specific pH levels. If you neglect to check your pond water’s pH, your fish will stress out and die. The dead fish release more organic nutrients into the pond water, allowing the algae to thrive.

pH test for pond water
pH test for pond water | Source

Algae, KH, and pH

KH is carbonate hardness. pH is acidity. These are water factors, you need to consider in maintaining healthy pond water. They influence the health and performance of your aquatic plants. They also provide benefits to your pond’s microorganisms.

You should know that your pond’s pH changes every day, throughout each day. It has low pH in the morning. As the day progresses, the pH increases because of photosynthesis. Respiration during the evening decreases the pond’s pH. This change in pH is known as the diurnal cycle. If you have Koi or goldfish in your pond, you should maintain a pH of 6.8 to 8.2. The fluctuation of the pH should not be more than 0.8 each day.

Once your pond accumulates excess nutrients, algae are surely to grow. When algae overpopulate your pond water, the pH rises. This is because of the increased process of photosynthesis. This keeps the aquatic plants to acquire the nutrients they need to make their own food. Specific types of algae find a high pH environment tolerable. As algae thrive, other pond organisms die off.

To put the pH in moderation, carbonates are present. They serve as the buffer to stabilize the pH levels in the pond. The carbonate levels should be 125 to 180 ppm (parts per million). You should first test the buffering capacity (KH) before you adjust the pH.

Test kits are available to test the KH level of your pond water. The units dh (degrees of hardness) or ppm (parts per million) are used to express KH. If the KH is lower than 125 ppm, you should add sodium bicarbonate and test after six hours. Stop adding sodium bicarbonate when you reach, or go slightly above 125 ppm.

Take note that the level of water hardness (more than 230 ppm) is found in well water. You can reduce the hardness by simply adding RO water, rainwater, tap water, or distilled water. You can also add acids to the water or filter it through a peat.

Remember that you have to balance the water condition. Many plants should be placed in and around the pond. The plants compete with algae for nutrients in the water. They also provide enough shade over the pond, preventing the algae from performing photosynthesis. As much as possible, do not over feed the fish. The following steps are an order:

  1. First, de-chlorinate the pond water.
  2. Test the pH and KH, and then adjust them to balance the water condition.
  3. Add your plants.
  4. Add the good bacteria.
  5. Wait for the pond water to age and accumulate more good bacteria.
  6. Add your pond fish.

Also, take note that as new water is added into the pond and bacterial activity consumes carbonates, you should always re-test the pH and KH during the growing season.

Comparison of pH
Comparison of pH | Source

Keeping an Eye on pH

Most pond and aquarium owners do not understand how to control pH. As you know, it is the measure of the water’s alkalinity and acidity. pH 7 is the neutral level in the 1-14 pH range. When the levels go up, the water is alkaline. When it goes down, the water becomes acidic. The pH scale is logarithmic. This can be best explained with an example. One is that pH 3 is a hundred times more in acidity, compared to pH 5. Another example is that pH 6 is about ten times more in acidity, compared to pH 7.

The same thing goes for alkalinity. The neutral pH is seven. If your water is pH 8, your pond fish are living in an alkaline environment, ten times more than normal. When tit rises to pH 9, your fish are in an alkaline environment, hundred times more than normal.

The rise and fall of the pond water’s pH influence the health and longevity of your pond fish. If you really want fish in your pond, then you should take time in finding out which species of fish can live in your pond’s pH level. Never combine fish, which require different pH levels to thrive. The incompatible pH in your pond will only result to stressed fish.

Biological filter
Biological filter | Source

Biological Filtration

Biological filtration is the key to a well-balanced pond or aquarium pH. This process of filtration involves a bacterial population, which converts ammonia into nitrites. The beneficial bacteria inhabit new filters and even rocks. This is how they efficiently remove nitrites and ammonia. If you have excess nutrients in your pond water, the filter can become overworked. You can monitor your biological filter’s efficiency by testing your nitrite and ammonia levels.

It usually takes months for the needed bacteria to grow in the biological filter. During this time, you should leave your pond empty of fish. Allow your pond to age first, with enough bacteria, before you incorporate fish. This usually takes several weeks. Start with a few strong fish before adding more slowly. This makes sure that the filter is not overwhelmed.

Healthy, happy Koi
Healthy, happy Koi | Source

How Fish Health is Affected by Water Hardness

Various fish have different requirements for water hardness. You should study your fish species well and know what level of water hardness is best to maintain. Goldfish and Koi require medium level of water hardness. Most pond fish species need 100 to 300 mg per liter of Ca Co3. The osmoregulation of fish is influenced by the hardness of your pond water. Fish are very much affected by the components of the water in which they live. Freshwater fish continuously take in water, while saltwater fish continuously expel water. Osmoregulation makes the fish maintain their internal fluid concentration. Some species of fish benefit from an increase in water hardness. The hardness prevents more influx of water into the bodies of each fish. Because of this, the fish do not have to exert so much effort in performing osmoregulation.

Your pond needs utmost care. Concentrate on the pond water’s condition and the algal population will always be regulated.

Koi and Water Balance


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