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Freshwater Aquarium pH

The pH scale is a measure of the degree to which the water in freshwater aquariums is acidic, alkaline, or neutral. The scale ranges from 0 to 14 with 0 being the most acidic, 7 being neutral, and 14 being the most alkaline. Most fish thrive in a pH range of 6.4 to 7.8. However, there are exceptions. The freshwater aquarium ph scale is logarithmic which means in simple terms that a very small change in value is a very large change in acidity or alkalinity. It is much more important that the pH of your fish tank remains constant. While a fish may prefer a pH of 7.2 it will most likely be perfectly happy with a pH of 6.7. However the same fish will become extremely stressed if you have a pH swing of 0.3 over the course of a day.

The best way to deal with freshwater aquarium ph is to acclimatize your fish to live in the ph that you provide and try to avoid sudden changes in it, i.e. keep it constant as far as possible. By constant, I mean no more than a 0.2 change in the pH during a 24 hour period.

As a side note, there are some freshwater species that require a particular pH when they breed. If you plan to breed a certain species, research the range of freshwater aquarium pH it finds acceptable to breed in. Some species are very forgiving, while others have a very tight range. This may be one of the only reasons you need to go for a specific freshwater aquarium pH.

Please read this article on Aquarium Test Kits for information on pH testers.

Factors Affecting ph

There are two main factors:

• Biological filtration As you already know, filtration is essential in a well stocked aquarium. Biological filtration removes the ammonia in your tank. It also tends to release carbon dioxide into the aquarium water and thereby reducing the tank pH.
• Carbonate hardness or kH is a measurement of the carbonate hardness of your water. A high kH (i.e. the harder your water) the better is the ability of your aquarium to neutralise added acids without significantly changing the ph. It is called your water’s ‘buffering’ capacity. Generally speaking, kH should be above 4.5.

Adjusting ph

Frequent water changes are the best way to keep the pH up to an appropriate level. As stated above you should acclimatise your fish to live in the ph that you provide but if it is necessary to change the ph for any reason then here’s how. How to Lower your freshwater aquarium pH

• Filtering water over peat
• Add bogwood to the tank
• Inject carbon dioxide CO2
• Use a commercial acid buffer
• Water changes with softened water or RO/DI (Reverse Osmosis/De-Ionized) water

How to Raise your freshwater aqaurium pH This should not be done lightly since as you raise the pH, you are making the ammonia in the tank more toxic to your fish.

• Aerate the water, to drive off excess carbon dioxide (CO2)
• Filter over coral or limestone
• Add rocks containing limestone to the tank or add crushed coral as a substrate
• Use a commercial alkaline buffer

Conclusion

It is much more important to have a stable pH than to have a specific value for your freshwater aquarium pH. To this end you should ensure that the kH of the aquarium water is somewhere around 5-6 dH which means that the water has adequate buffering capacity. Adjusting the freshwater aquarium pH can be dangerous to the fish as swings of just 0.3 in a day can be deadly. Therefore, unless you have a specific reason for doing so, it is better to acclimate the fish to your tap water’s pH than to adjust your pH to fit the so called preference of your fish.