Maintaining the pH of aquarium water

Test Strip for pH

What Is pH?

Since "H" is the atomic symbol for the hydrogen element, the "H" in pH is usually capitalized. The acronym pH stands for "power of Hydrogen." The pH scale ranges from 1 to 14, and it measures the acid-base balance of a solution.

Atoms of hydrogen and oxygen make up water, or H 2 O. A pH value of 7.0 is assigned to neutral water because it has an equal number of hydrogen ions (H +) and hydroxide ions (OH -). When minerals and compounds are dissolved in water, the balance of those ions can alter from neutral to acidic or basic depending on the ratio of hydrogen to hydroxide ions. In contrast to basic solutions, which have a pH value greater than 7.0, acidic solutions have a pH value lower than 7.0. The water gets more acidic or basic (respectively) the more these levels deviate from 7.0.

What Is Normal pH?

There is no pH that can be considered "normal" for all fish. The ideal pH for fish varies by since they are born in ponds, rivers, streams, lakes, and seas with varied pH values. require a pH of 8.0 or higher that is basic. African cichlids are frequently found in lakes with pH levels higher than 8.0. Brazilian riverine tropical fish may survive in waters with a pH of 5.5 or lower.

Remember that pH is dynamic and varies over time. In fact, it could alter even within a single day. In the natural world, pH often changes during the day and night as a result of photosynthesis and plant respiration. As fish are added or withdrawn, water is added or altered, and the biological processes in the aquarium change, the pH may also vary.

Preferred pH of Common Freshwater Fish

  • Angelfish 6.5 - 7.0
  • 6.0 - 6.5
  • Goldfish 7.0 - 7.5
  • Harlequin Rasbora 6.0 - 6.5
  • Hachetfish 6.0 - 7.0
  • Neon Tetra 5.8 - 6.2
  • Plecostomus 5.0 - 7.0
  • 6.0 - 7.0
  • 6.0 - 6.5
  • Danio 6.5 - 7.0

How Important Is pH?

Significant pH changes are particularly hard on young and sick fish. In a number of species of fish, breeding occurs only within a specific pH range.‚Äč

Knowing your water source's pH while setting up a new aquarium can help you determine whether it is suitable for the fish you wish to maintain. When setting up an aquarium, owners should keep in mind that some species, like discus and some other cichlids, thrive in extremely specific pH ranges.

The pH levels must be the same when transporting fish from one tank to another. Many fish losses that happen when fish are brought home from a pet store are attributed to abrupt pH changes. Because they are so sensitive to pH fluctuations, neon tetras are readily shocked when transferred.


Fish can be harmed or even killed by pH changes, especially abrupt ones. The toxicity of substances like increases when the pH rises. It is a crucial aspect to keep an eye on when a new aquarium is being broken in.

How Often Should I Check pH?

To identify trends before they become an issue, the pH should be checked at least once a month, ideally every two weeks. Keep a journal of your test findings for future use. Keep in mind that testing at different times of the day might provide different results even when nothing is wrong since pH can fluctuate depending on the time of day. Testing need to occur at the same time of day, ideally in the afternoon, for this reason.

Testing the pH should be done if a fish becomes unwell or perishes. If the tank is given medicinal therapy, the pH should be assessed at the start of the treatment, on the last day of the treatment, and once more a week afterwards. When the pH begins to deviate from the ideal range for the fish, make water changes as necessary.

Testing your water right before buying new fish is also a good idea. Ask the store where you are buying the fish what the pH of their water is. It's crucial that the pH of the water the fish are now in is similar to the pH of your house water (preferably within 0.2 units above or below the home pH value).

Should pH Be Altered?

I advise adhering to the proverb "If it ain't broke, don't repair it." If your water tests at 7.0 and the textbook states 6.4 is the ideal pH for fish, don't take immediate action. It is recommended to leave the pH at your local tap water's level as long as it is stable and the fish don't appear to be in danger. Additionally, the majority of aquarium fish marketed today are grown in facilities that do not maintain the pH of the water in their native environment. So most freshwater fish may be kept safely in a pH range of 6.8 to 8.0.

The issue has to be fixed if the fish are not prospering or if testing reveals a trend, such as a consistent rise or fall in pH. Pet stores provide commercial goods that may be used to raise or reduce the pH of your local tap water as needed. Your greatest bet is always to maintain water actively. The most crucial things you can do to maintain constant are periodic partial and gravel cleaning. The pH will progressively decrease as the alkalinity (carbonate) in the water is utilized by the biological filter bacteria that break down fish waste over time (become more acidic). This may be avoided by doing to get rid of the water with a lower pH and by introducing new, dechlorinated water with a greater alkalinity to increase and stabilize the pH.


"Aquarium Water Quality: pH. Florida Department of Agriculture and Consumer Services.", "pH. United States Environmental Protection Agency." ;