The pH scale is a measure of the degree to which your aquarium’s water 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.   The majority of fish will happily live in water of pH between 6.4 and 7.8 but there are some exceptions.

Because pH is a logarithmic scale a small change in pH means a very large change in acidity or alkalinity.

It is changes in pH value that affect your fish much more than the actual pH value.  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 be most unhappy if over the course of a day it experiences a change in pH of 0.3.

The best way to deal with pH is to acclimatise your fish to live in the pH that you provide and try to keep this constant as far as possible.   Constant measns that the pH should nt range by any more than 0.2 over 24 hours.

In some cases breeding only takes place at a particular pH value.   If you plan to breed a certain species, research the range of pH it finds acceptable to breed in.    Some varieties are easily pleased while others have a very small range.   This is probably the only good reason why you might want to aim for a particular pH value.

Factors Affecting pH

• Biological filtration As you already know, filtration is essential in a well stocked aquarium.   Biological filters reduce pH because they release carbon dioxide into the water.
• Carbonate Hardness 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 water able to neutralise added acids without significantly changing the pH.   When you water has a kH of above 4.5 it is said to have a good ‘buffering capacity’.

Adjusting pH

Regular water changes (which you should be doing anyway) is the best way of keeping the pH reasonably level.

Acclimatising your fish to the pH provided is the best way to deal with pH but you can change it as shown below.

How to Lower the 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 the 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 use a coral sand substrate
• Use a commercial alkaline buffer

Conclusion

Rather than aim for a specific pH value you should take steps to ensure a stable pH.   To achieve this the kH should be around 5-6 dH in order for the water to have enough buffering capacity.

Even small swings of more than 0.2 pH in a day can cause your fish to die.   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.

For more information on freshwater aquarium pH go to my website www.freshwateraquariumsecretsonline.com