Pond pH... Fluctuating pH is Normal

Page Summary: pH is the most widely discussed property of koi fish pond water. For some reason pH is stressed over and above any other water property despite the fact that is is probably the least important water quality parameter in almost all pond keeping environments for the hobbyist fish keeper. pH is certainly the most difficult to control since every location will quite possibly have natural water supplies differing in pH. This alone means that nature is quite able in most cases to deal with pH variations. Nevertheless pond keeping is a hobby and part of that hobby is to measure changes in a fish ponds environment. Heres my golden rule if you decide to measure pH: measure pH at same time every day since pH changes with time of day. Plot the results and look for long term trends which may indicate real changes. Under no circumstances start to try to control pH by adding chemicals to water without this long term information. Almost certainly you will will create more problems than you will solve by trying to adjust pH. In the rare cases where pH rises to levels of 9 and above and there is poor biofiltration then pH is definitely a real problem and action is required. This could happen in really bad suspended algae ponds.

Why pH is important

An abbreviation for "potential of hydrogen", pH is a measure of waters acidity or alkalinity. Whether it is swimming pool water or pond water, we dont want it to be too alkaline or too acidic. Acidic water can be particularly harmful for both fish and humans. This is what will sting our eyes and damage our skin. Acidic water can also damage the gills of koi and goldfish.

Fortunately we can measure the pH of water according to a logarithmic number scale, and can immediately pick up if the water is either alkaline or acidic. The pH scale goes from 0 to 14, with 7 being neutral, and perfectly balanced.

Test kits utilize a universal indicator that changes colour when it is put into water, according to the strength of acidity or alkalinity. So, for instance, if the indicator goes red, the pH is highly acidic (0-3) and if it goes violet, it is strongly alkaline (11-14). Green shows that the water is perfectly neutral, while yellow shows it is slightly acidic (6), and turquoise shows that it is a little alkaline (8). While some test kits state that pH should be stable between 7.0 and 9.0, in fact it is best to keep the level closer to 8.0. It shouldnt fall below 6.8 because the acidity really can be damaging.

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The natural environment of koi is alkaline water. While they will tolerate some swings within the lower alkaline range, they cant tolerate major swings or swings from alkaline to acidity.

In general fish prefer alkaline waters because this type of higher pH water is more suitable for plant growth and thus a whole spectrum of aquatic life. Compare the barreness of acidic highland streams compared to rich fertile rivers and lakes situated within dolomitic or limestone regions.

Why pH fluctuates

Photosynthesis, which is a natural process for all forms of plant life in and around the fish pond, will naturally increase pH. Because photosynthesis takes place during the day, the pH will therefore be higher during the day. When carbon dioxide (CO₂) is released back into the pond at night, the pH will drop. This is caused by respiration (the opposite of photosynthesis) of both plants and animals. If the rate of photosynthesis and respiration are balanced, then the pH will fluctuate slightly day and night, but overall it will remain stable.

A more alarming culprit comes in the form of nitrates and ammonia. When nitrification (or biofiltration) takes place, the nitrifying bacteria remove the hydrogen atoms in the water and replace them with double the number of oxygen atoms. This makes the pH fall and become acidic – which, as we have said is dangerous.

How to stabilize the pH in a koi or goldfish pond

In the wild there are natural compounds that act as buffers that generally prevent water becoming too acidic. The most common of these is calcium carbonate which is present in various forms including limestone, oyster shells or tufa rock. So this is the type of material that you will need to add to a koi fishpond with water that is acidic. A very simple way to do this is to add calcium carbonate to your filter. You can buy this in a mesh bag from any good fish pond supplier.

If you get a low (and therefore acidic) pH reading in your koi pond, you need to act quickly. Often the best thing to do is to partially change the water in the fish pond. Ideally use treated mains water rather than borehole or rain water. This is because municipalities generally treat water so that it is slightly alkaline because acid can easily corrode pipe work.

Thereafter be sure to use a test kit to measure the pH in your koi pond regularly. You should also test for nitrates and ammonia (that should never be present), and to see what the oxygen levels are.

On this site we dont pretend to be "Koi Crazy" despite the fact that you will see I refer to koi more often than not.

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