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How to Treat and Prevent a Pond pH Crash

12th March

What is a pond pH crash and why is it dangerous?

A pond pH crash is when a pond experiences a sudden and dramatic change in pH levels. Typically, this is when a pond’s pH drops below 6.5. A considerably acidic environment compared to the recommended neutral pond pH measure of 7/7.5.

pH crashes are important to avoid because of the damage they cause to the natural biological balance of ponds, that work to sustain life. Fish, (aquatic) plants and wildlife suffer fatal consequences as a result of big drops in pH.

Acidic pond water also makes effectively maintaining clear and healthy pond water difficult. Such conditions would also kill off the beneficial bacteria that would otherwise remove the build-up of sludge, green water algae and improve the activity of biological filter systems.

What causes and increases the risk of a pond pH crash?

Various factors can cause a pond’s pH to crash. However, the underlying problem is unstable water. It’s quite normal for a pond’s pH to slightly fluctuate throughout the day. For example, if you tested your pond water in the morning, you will typically find your pond’s pH at its lowest.

The stability of your water against pH crashes is determined the measure of carbon hardness (KH) levels in the pond. Carbon hardness determines to what extent a pond’s pH will fluctuate. The lower the KH levels are in your pond, the higher the risk of a pH crash. This is because the water is more susceptible to bigger drops/fluctuations in pH in short spaces of time. Hence why many pond owners experience what’s commonly known as an “overnight pH crash”.

Other factors that also increase the risk of a pH crash:

Small ponds, particularly those containing less than 9,000 litres of water are more likely to have unstable water parameters and so are at much higher risk of the damaging effects of a pH crash. That’s because sudden changes in a small pond will affect the whole body of water, while in a bigger pond, only a specific area is affected. If you’re not sure how much water your pond contains, find out now with our pond volume calculator.

Areas or periods of heavy rainfall or snow also cause pond pH crashes. Natural rainfall is slightly more acidic (with a pH averaging 5.6) than normal range of stream water. Which would have a neutral pH reading around 7.0. Thus, large amounts will alter a pond’s pH.

Due to the low level of carbonates present, areas of soft water are also at higher risk of pond pH crashes. It’s important to be aware of the type of water supplied to your areas. Especially when it comes to conducting pond water changes. Without enough carbonates, tap water is unstable. Making ponds sensitive to changes in pH.

Common signs of a pond pH crash

Pond pH crashes are not visible to the naked eye.

However, there are certain symptoms that act as warning signs in your pond:

The sudden death of fish or wildlife. Fish either resting at the bottom of the pond or gasping for air at the surface. Overgrowth of pond algae. Lethargic fish activity. Damaged aquatic plants. Fish with slimy skin. Changes in water clarity. Pond Odour.


While these are common signs of a pond pH crash. Without testing your pond water and knowing the ideal pond water parameters, you’re only playing a guessing game.

How to treat/prevent a pond pH crash

The best way to treat and prevent a pond pH crash is to use pond pH buffer Pond Equaliser. A unique treatment that not only stabilises key water parameter (pH, KH and GH levels) for up to six months. Containing beneficial calcium, it also helps to remove toxic heavy metals and ammonia. Improving your pond’s overall water quality!

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