pH

The Importance Of pH In Aquarium And Pond Keeping (NEW!)

pH Chart

The pH (acidity/alkalinity) of the water is an important indication of one factor of water quality in aquarium and pond keeping, referring to how acid or basic the water is.  the measuring scale that is of concern to aquarists and pond keepers is between 5 and 9 on the pH scale, with below 7 acid, 7 neutral, and above 7 basic (which is also often referred to as alkaline).  Below 5 or above 9 is too extreme for most fishes and aquatic invertebrates.  The measurement scale is logarithmic, so a pH difference of 1, such as between 6.0 and 7.0, is 10 times more basic than pH 6.0, and 100 times more basic between 6.0 and 8.0.  A pH change of  even 0.1 or 0.2 can be of concern to keeping fishes and aquatic invertebrates. 

Tropical Marine Fishes,  Invertebrates, and Plants
Marine tropical water conditions around the world, particularly for tropical coral reefs, vary in pH only in the range of 8.2-8.3.  In fact the traditional natural average has been 8.3.  With what appears to be global warming, and increased fresh water in the oceans, the pH is slightly declining towards 8.2., apparently to become currently established at 8.2.  Therefore, there is the need to keep marine conditions in tropical marine aquariums and ponds as close to this range as possible, because in nature there is only this amount of variation on most tropical coral reefs.

The commercial breeding of marine tropical fishes and invertebrates and plants has only been in recent decades.  Only about 50 species of coral reef fishes and about the same number of coral reef invertebrates (mainly coral species) have been commercially bred for aquarium keeping.  Most popular coral reef fishes and invertebrates for marine aquariums are wild caught and come from a relatively unvarying natural environment.  Therefore, there has not been the opportunity through inbreeding to develop strains of marine coral reef fishes and invertebrates that have a wider adaptability to changes in pH or other water conditions.

Therefore, the monitoring of marine pH - to keep it within the 8.2-8.3 range - is very important.

Tropical Freshwater Aquarium Fishes, Invertebrates, and Plants 
Natural freshwater conditions vary widely, depending upon many factors around the tropics.  For example, let us consider the conditions in eastern South America for the major Amazon and Orinoco river systems covering thousands of miles in geographic area, and home to many of the fishes that are popular in aquarium keeping.  In the wet season these rivers flood, inundating jungles and plains and forming broad lakes.  the pH gets up to 8.2 or more, which is the natural pH for large open bodies of water such as lakes and the ocean.  In the dry season the rivers dry up, becoming disconnected in many parts of their distribution, leaving short river sections and isolated ponds, all of which can become highly acid to pH 6.0 or less.

There is also the consideration that each year when the rivers flood, inundating jungle growth and the roots and trunks of trees where the ground is flat, tannins are leached out of the vegetation that in the dry season can increase the acidity of the water. 

This means that the many kinds of fishes and other aquatic life in much of the Amazon and Orinoco have to undergo major changes in water quality, including pH, every year of their lives.   To characterize these fishes (or invertebrates or plants) as requiring a particular pH depends on the water conditions and the time of year that is being considered, not to which the fishes and other inhabitants are capable of naturally adapting.  Therefore, attempting to control the pH of freshwater aquariums and ponds is considerably less constrained than for marine aquariums.  When it becomes important is when controlling water conditions to induce spawning in fishes, which in nature is usually during the season of highest water flow. 

There is much confusion about what pH many freshwater tropical fishes should be kept at.  Often this is from information about the time of year for those fishes caught during the dry or wet seasons, indicating a low pH as "natural" when reporting for the dry season, and a high pH as "natural" when reporting for the wet season.  Neither tells the whole story.  

What is known is that whatever pH is established for freshwater fish keeping should be maintained within a narrow range.  Aquarium keeping is not like out in the wilds.  The fish do better when the pH is not vacillating.  Even though their ancestors may have came from waters with a wide range of pH through the year, those now kept in aquariums are less tolerant.  A pH range of less than 0.2 pH is going to serve most freshwater fishes very well and avoid the strain of pH shock from varying acidity/basicity. 

Also, it needs to be realized that most of the freshwater tropical fishes in aquarium keeping are commercially raised, most often in countries far removed from their original habitat, and with different water conditions than what was natural for them.  These raised fishes have had to adapt to conditions, including pH, entirely different from those from what there  were for their wild-caught predecessors.  In fact some of these species are now rare in their native country, or are from areas that cannot be accessed because of hostile conditions for the people there.  For example, the Emperor Tetra (Nematobrycon palmeri), native to Colombia, is rarely now exported from Colombia because its home region is turbulent with drug dealing and inaccessible.  This tetra is now primarily bred and raised in Southeast Asia from stock that originated decades ago from Colombia.

African cichlids from the Great Lakes of Africa originated from natural alkaline water conditions that mostly ranged at the high pH of 7.8-9.6.  Now most are bred in other countries with water nearer neutral 7.0.  These raised cichlids, now accustomed to the water being at a lower pH than their natural habitat, are now adapted entirely to different lower pH conditions than their wild-caught predecessors.

The Importance of Using pH Tests To Monitor Water Conditions and in Making Adjustments in Water pH
The answer is clear in tropical marine conditions.  The pH for tropical marine aquariums should be kept stable at 8.2-8.3.  The most likely deviation in pH is going to be by the water becoming more acid as the aquarium water ages.  To stabilize the pH, the aquarist should use water changes and/or pH buffers in the water to  maintain the pH at 8.2-8.3.

For freshwater fishes it is best to aim for a stable pH near neutral of about 7.0-7.2.  Most freshwater fishes are raised, not wild caught, and are already adapted to this level of pH.  What has become known over time, despite what their natural pH water conditions might have been, is that it is best to keep the pH stable, because even one tenth of a pH change is a doubling of pH on its logarithmic scale.  This is a substantial change in acidity/alkalinity for the fish and invertebrates in that water.  As mentioned for marine aquariums, the proper pH can be maintained through water changes and/or using buffers that stabilize the pH, such as for freshwater at 7.0. 

Therefore, regular testing for pH is highly recommended to be sure that the pH is being maintained at a stable level, whatever is decided upon as the correct pH.

Freshwater Pond Fishes
While pond fishes, such as koi and goldfish are adaptable to a wide range of acidity/alkalinity, it is best to keep them within a pH of about 7.0-7.5, with a primary consideration to keeping the pH stable within a range of about 0.1-0.2 pH.  This can be done with the help of water changes to reduce the acidity over time, and the use of pH blocks that gradually dissolve over time keeping the pH constant.

What The Proper Test Kits Are For Measuring pH Alkalinity/Acidity Of The Water
The topic of water quality test kits is an important subject in aquarium and pond keeping, and is covered separately in a series of Kordon Articles listed under the heading "Water Quality Test Kits".   Most of all read the Kordon Article "The Truth About Water Test Kits -- What You Need To Know"

Fortunately, there are more pH test kits out there that are accurate enough to be of help than there are of other kinds of water tests.  Test reagents go out of date over time so be sure that the one you choose is still active.  It is recommended to choose a test kit that indicates the expiration date for the reagents.  Also consider buying packets of reagents when you run out of reagents, rather than all new test kits.  For further information on pH test kits, see Kordon products listed on the Kordon home page for low range fresh water pH,  high range fresh water pH, and marine pH AquaTru Test Kits