Aquarium pH

By Madhu Soodhanan of India

Whenever one surfs the net or refers to a book about fish-keeping, pH would be a short-listed, important point of concern. Many of us have read articles/books saying fishes are not tolerant to wide pH ranges or pH fluctuations. But is pH that important in fish-keeping? Is it easy to handle pH?

What is pH?

pH is a logarithmic scale of the proportion of H+(Hydrogen) and OH-(Hydroxyl) ions ranging from 0-14, with a neutral value of 7. When the H+ ion concentration is higher, water is said to be acidic; when OH- concentration is higher it is said to be alkaline. In other words if the concentration of dissolved minerals is high then pH is high and vice versa. pH is also dependent on various factors like water hardness, dissolved minerals, oxygen level and many more.

Its importance

Many believe that even the smallest change in pH is highly stressful to aquarium fish. You might have come across volumes saying that a pH of 6.5 is 10 times more acidic than a pH of 6.6. Many have a deep rooted feeling that all fishes in the wild live in perfectly stable and narrow pH ranges and fishes cannot adapt to changes in pH, and some say that fishes will perish immediately in case of any pH changes.

What happens actually?

In the wild, pH is not as stable as many of us think. It fluctuates considerably. In Indian waters I have observed higher pH during day times and lower during nights. Also, pH is lower in autumn and higher in spring. In autumn, dead leaves fall and decay in watersheds leaching out acids like tannin, which acidifies the water. In spring there are more monsoon rains, hence more oxygen dissolves and therefore the pH pumps up.

In aquaria, pH is not perfectly stable either. pH changes in accordance with aeration, decoration, gravel, temperature, nitrate content, dissolved minerals and many more.


So pH is not nearly as important as it is believed to be. What I would suggest is that if you intend to get so called acid-loving fish like discus or tetras don't rush or panic to bring down the pH, or in the case of Malawians don't rush to lift the pH to around 9. Stay cool and your fish can adapt to your tap water, and don't spend more on water softeners like RO units or resins or water hardeners.

I don't advocate you not to change your pH deliberately, but I would advocate you not to make alterations in pH in a panic. If you are so particular in bringing down pH you can rely on peat-filtration or a piece of driftwood. Instead of spending on RO or other resins, you can spend that money on a bigger tank. Try to keep your pH fairly stable. If you are so concerned about your fish's health, consider regular water changes. Don't panic and get into a mess as fishes face more nightmares and harsh conditions in the wild than in home aquaria. I would also advocate against using a pH lowering chemical until you know its ingredients and its working, and NEVER TEND TO INCREASE OR LOWER YOUR pH RAPIDLY.

Happy fish keeping!

Related Tropical Fish Articles
The Aquarium Nitrogen Cycle
Cloudy Aquarium Water