pH is an acronym which stands for ‘potential of hydrogen’.  The precursor to pH was a general concept of acidity and alkalinity shared by Greek philosophers Socrates and Aristotle.  They could see differences between acid and alkaline substances and their affect of other substances.

The pH scale, as it is known today, was developed in 1909 by a Danish biochemist by the name of Soren Peder Lauritz Sorensen.  Mr. Sorensen defined pH as the negative logarithm of the concentration of hydrogen ions (H+) in a solution.  He devised a scale to represent the acidity and alkalinity of a substance, with pH 7 being neutral.  Numbers below 7 indicated acidity, and numbers above 7 indicated alkalinity.

Initially, measurement of pH was accomplished using litmus paper which changes color depending on the acidity or alkalinity of a solution.  More recently, electronic measurement tools have been developed with significantly greater accuracy.

pH has found applicability in many fields.  It has found widespread application in numerous fields. In chemistry, pH is used to measure and control the acidity or alkalinity of chemical reactions. In biology and medicine, pH is important for understanding enzyme activity, cellular processes, and the acid-base balance in the body. pH is also crucial in environmental science, water quality testing, and agriculture.

Today, pH continues to be a fundamental parameter used in research, industry, and everyday life to assess and regulate the acidity or alkalinity of substances and solutions.

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Different fish species and invertebrates have specific pH requirements to thrive. Some prefer acidic conditions, while others prefer alkaline conditions. By monitoring and adjusting the pH, aquarists can foster an environment that is suitable for the specific species they are keeping. Maintaining the appropriate pH range helps prevent stress and health issues in the aquarium inhabitants.

pH affects various biological processes in the aquarium, including the function of enzymes and the efficiency of biological filtration. Maintaining the optimal pH range supports the natural biological processes and overall biological balance in the aquarium.

In planted aquariums, pH influences the availability of nutrients to plants. Some nutrients are more readily available at specific pH levels. Monitoring and adjusting the pH within the optimal range for the plants being cultivated can support their growth and overall health.

pH is closely tied to the acid-base balance in the aquarium. Sudden or significant fluctuations in pH can disrupt the acid-base equilibrium, leading to stress and potential harm to the aquarium occupants. Monitoring pH helps ensure a stable and suitable environment for the aquatic life.

pH is one of the key parameters used to assess overall water quality in the aquarium. Fluctuations in pH can indicate changes in water chemistry or the accumulation of harmful substances. Regular pH testing and maintenance help ensure good water quality and a stable living environment for the aquarium occupants.

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Many in the aquarist field portray pH as a problem that must be corrected.  As seen above pH is actually just a marker that should be used by the aquarist to maintain an optimal water environment.

Understanding what causes pH fluctuation may provide insight as to what remedial action should be taken to manage pH levels.  Here are a few causes of pH fluctuation in aquariums.  Examine them to see which might have applicability to your aquarium.

Water source: The pH of the water you use to fill the aquarium initially determines the starting pH. Tap water can have different pH levels depending on your location. Some tap water may have high or low pH, which can affect the aquarium’s pH.

Fish waste and respiration: Fish produce waste in the form of ammonia through their respiration and excretion. Ammonia is toxic to fish and can affect the pH balance. Bacterial processes convert ammonia to nitrite and then nitrate. High levels of nitrate can lead to a decrease in pH.

Biological filtration: The aquarium’s biological filtration system breaks down waste products, such as ammonia and nitrate, through the nitrification process. This process can release hydrogen ions, which can lower the pH over time.

Decomposition of organic matter: Uneaten fish food, dead plants, and decaying organic matter can release acids during decomposition. These acids can lower the pH of the water.

Carbon dioxide (CO2) levels: High levels of carbon dioxide can cause the water to become acidic. In planted aquariums, photosynthesis by plants during the day can deplete CO2 levels, resulting in higher pH. At night, plants consume oxygen and release CO2, leading to lower pH.

Substrate and decorations: Certain substrates and decorations, such as driftwood, rocks, or shells, can leach chemicals into the water, affecting pH. For example, driftwood can release tannins, which lower the pH.

Chemical additives: The use of chemicals like pH adjusters, buffers, or medications can impact the pH levels if not used correctly. Overdosing or improper use of these additives can cause pH fluctuations.

Sudden changes to pH should be avoided if at all possible.  Make sure of the pH measurement before making any adjustments.

If the aquarium is planted (has live plants) there will be a natural fluctuation in pH due to the CO2 levels present in the water, changing from day to night as the plants consume CO2 and release O2.  Take measurements of the water at mid-day ( 4 hours after aquarium lighting is enaled).

Before making any changes research your occupant’s preferred pH range: Different species have specific pH preferences and tolerances. Make sure you understand the pH requirements of the occupants in your aquarium to avoid creating a harmful environment.

Some natural materials can help adjust pH levels. For example, adding crushed coral or limestone to the aquarium can raise the pH by releasing calcium and carbonate ions. Driftwood or peat moss can help lower the pH by releasing tannins and organic acids. However, natural methods may take time to have an effect, and their impact may vary.

Introducing an aeration stone to the aquarium will help to release CO2.  This will  cause the water be become slightly less acidic.

Another way to change pH is to perform a partial water change.  If the pH is too high, you can use reverse osmosis (RO) water or distilled water to dilute the tap water. If the pH is too low, you can use tap water treated with a water conditioner that stabilizes pH. Gradual changes are recommended.

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As we have seen, pH is an indicator metric.  pH gives us a flag that some investigation should be performed.  Keeping a notebook in which pH levels and other test levels are noted will help you make smart decisions as to how to address pH levels in the aquarium.

Understand the relationships between pH and ammonia and pH and nitrite/nitrate levels.  Make observations regarding sediment and dead plant material and how it affects pH levels.  Monitor the volume of food given to the aquarium occupants.  Biological activity breaking down excess food contributes to pH level  fluctuations.

As an aquarist you are a scientist that is continually investigating the causes for changes in the aquarium water.  Nobody knows your aquarium better than you – well except of the occupants of the aquarium.

If a change is needed, make it a slight one, and then retest.  Write in your notebook what change you made and what affect it had.  Keep track of your water chemistry and your actions to modify it.

Over time you will be able to establish the rate of pH change and rate of ammonia and other water metrics.  This will help you to make just the right modifications to keep your aquarium pH in the correct range for your aquarium occupants.