Koi Pond pH Buffers: How do They Work?

Page Summary:  In some ponds depending upon type of water used in the area water may already contain some buffering effect (eg ponds whose water source is limestone rich ground). Buffering is a term which essentially means that the movements of pH within a pond environment do not swing to extremes. There is always a natural pH swing during a 24 hr period but in water with low buffering (acidic waters)the tendency will be for the pH to vary more widely than for most fish ponds. Even this movement will not normally be a problem except possibly when ammonia is present (bad biofiltration).


What we often don’t realise when we marvel at the beauty of a thriving koi fishpond is that there are thousands of micro-bioreactions taking place that, although invisible to the naked eye, are responsible for the health and well-being of our treasured koi or goldfish.

When certain treatments are added to a garden fishpond, they also operate on an unseen level, ensuring that our pond’s water quality remains in a stable condition. Two common additives are clays and buffers which instantly interact with pond water on a molecular level. As a koi keeper, it is helpful for you to know exactly what happens when you add any of these two additives.

What is a Water pH Buffer?

A helpful analogy when attempting to understand what a buffer does is to think of it as a sponge that works by soaking up free hydrogen ions, thereby stabilising pond water pH. Therefore, a buffer is any material or compound that behaves in this way, with the most common buffer being calcium carbonate or matter which contains calcium carbonate like calcified seaweed, limestone chippings or cockleshell.

How Does a Buffer Work?

The benefits of good water quality cannot be overemphasised. A pond’s pH is especially important in this regard.

Ideally, your pond’s pH should remain between pH7 and pH9, as extreme fluctuations in pH can have negative side-effects on the health of your fish. Normal fluctuations during a 24 hour period say between 7 and 8 are quite normal (see pH detail at end of article)

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What is pH? It is a measure of the quantity of free hydrogen ions (H+) in your pond water. The more H+, the more acidic the water will be and the lower the pH. This is where buffers come in – to stabilise the pH.

Compared to a natural pond which experiences an inflow of freshwater and the inherent presence of certain minerals, a constructed koi pond has a higher stocking rate and significantly less contact with natural minerals and diluting water. It is therefore inevitable that a manmade koi fishpond’s pH will begin to drop.

Biofiltration processes are taking place all the time as your koi excrete ammonia which has to be processed into nitrite by bacteria. This process causes H+ to be released, thus making the water more acidic. Another factor which influences the acidity of the water is respiration which releases carbon dioxide that combines with water to form carbonic acid. It’s not only your koi that respire, but also the heterotrophic bacteria and pond plant life. It goes without saying then that the acidity of your pond needs to be addressed.

Buffers work by attaching to free hydrogen ions (H+). When hydrogen is unattached, it can cause the pH of your pond water to drop, but when attached to another compound then it will no longer affect the pH. Calcium carbonate, a common buffer, can be placed in you filter to react and bond with free hydrogen ions to form calcium bicarbonate, a soluble compound that cannot influence pH. What this essentially means is that you can protect your koi pond against fluctuations in pH by keeping undissolved calcium carbonate in your filter.


Dont stress over pond pH and Testing Koi Pond pH

Interpet Koi Pond Test Kit

I will make a few very important points here which should be taken very seriously by anyone contemplating measuring pH in a koi pond and then TAKING ACTION based upon the measured result from testing the koi ponds water. If you test do it reliably... Interpet lead this pond water testing field of the koi keeping hobby

  1. pH of koi pond water will vary depending on time of day measurement is taken and especially if plants are in the pond. This means if you take a pH at 9am it will not be the same as a pH taken at 6pm. This single piece of information therefore must never be the information relied upon to make fundamental decisions
  2. pH is notoriously difficult to measure even in a laboratory with sophisticated instruments let alone in a koipond or fish pond using a piece of litmus type paper or a vial with coloured scales on it.
  3. If you must measure pond pH and this is a great part of the hobby then take the pond pH at the same time every day and plot the result on a graph. So now what youre looking for is not a single pondwater result but rather a pH trend in the pond water that you can use to sensibly consider a pH strategy.
  4. Very high pH in a koi pond is a serious threat to the well being of koi when levels reach about 9.5 because at this pH level ammonia which is a natural metabolic product of the koi and its existence becomes extremely poisonous
  5. It would be extremely rare for a koi pond to reach dangerous pH levels but could well occur in koi ponds with serious algae problems

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