Articles > General Guides > Water pH Explained
Water pH Explained
Published by Fishy-Fishy on 15/07/2007 (24139 reads)
FK member Fishy-Fishy explains how water pH is important and offers some options on how to alter the pH in your tank.

You don’t need to be a scientist to successfully maintain an aquarium, but a basic understanding of how water chemistry affects your fish will make life a lot easier for you and a lot better (and longer!) for your fish. This article will explain a few of the basics you need to know about pH and how it relates to your fish.

What does pH mean?
pH stands for ‘potential of hydrogen’ and is a measurement of the acidity or alkalinity of a substance. The scale runs from -1.0 (Hydrochloric acid) to 13.9 (caustic soda) although most substances will fall between 1 and 9. Higher numbers are alkaline substances and lower numbers are acidic substances. The pH scale is logarithmic, meaning that pH 8 is ten times more alkaline than pH 7 and a hundred times more alkaline than pH 6. pH 7 is considered neutral as this is the pH level of pure water.

Buffers and Reserve Alkalinity
Buffers are solutions that prevent the pH of the water from rising or falling. These can be present naturally in water but are not present in distilled water, so if an acid or alkali is added to distilled water then the pH will change straight away.

Reserve alkalinity is the excess amount of alkali compared to acid. For example, if the amount of acid and alkali is equal or if the amount of acid is more, the water sample has no reserve alkalinity. If the amount of acid exceeds the alkali by 3, then the reserve alkalinity is 3.
If an acid is added to water with reserve alkalinity then it is neutralised by the excess of alkali. However, this can be exhausted. The filtration process produces acids so it is important to do regular water changes to refresh the supply of buffers.
If an alkali is added to a sample with reserve alkalinity but few buffers then the alkalinity will rise.

pH in the aquarium
Since the pH of water habitats varies around the world, different fish have different pH requirements.
Water that is too acid or alkali can hurt or even kill a fish so it is important to get it right. Symptoms of acidosis (pH too low) include erratic behaviour such as darting and jumping, usually followed by death. Symptoms of alkalosis (pH too high) include excess mucus production, gasping and sometimes dropsy. Since these symptoms can indicate other illnesses it is important to test the water to determine the reason for the behaviour.
Acidosis and alkalosis can be chronic (pH changes slowly over a long period of time) or acute (pH changes quickly). To treat either chronic alkalosis or acidosis, you should gradually correct the pH of the aquarium by no more than 0.2pH units per day. To treat acute alkalosis or acidosis, should any fish survive, you should alter the pH in the aquarium immediately to its correct level.

Changing the pH of tap water
This can be very difficult and all too often can result in fish illness or death. Commercially available products can be added to alter the pH of tap water. Although these contain buffers, all tap water is different and therefore the results can be variable. Some recommend that you add the product directly to the aquarium, which can be potentially dangerous- if you accidentally add too much then your fish could become ill or die. Sudden changes in pH can be very damaging for fish, even if the water they were previously in was too acidic or alkaline for them.
Side effects such as algae growth have also been reported when using these products.

Before attempting to change the pH of your tap water, check that it is totally necessary. Unless you are keeping very delicate freshwater fish such as discus, or marine fish then you probably don’t need to change the pH at all. If you really do need more acidic or alkaline water then RO water with added minerals is a much safer option. ALWAYS check the pH of any water before you add it to the aquarium, especially if you are attempting to change it.

Getting it right
Here are some options for achieving the right pH for your fish-

1) Match the fish to the water.
Check the pH of your tap water and choose your fish accordingly.
Advantages- This method is the cheapest and most convenient way to ensure your fish have the correct pH.
Disadvantages- Your choice of fish will be vastly limited, especially since most tap water in the UK is alkaline and many fish need slightly acidic water.

2) Choose fish that have been acclimatised.
A great number of fish have been bred in captivity or are hardy enough to withstand a slightly higher or lower pH than they would have in the wild. Ask at your local fish shop where the fish have been bred and what their current water readings are.
Advantages- Again, this method is cost effective and convenient.
Disadvantages- The choice of fishes will be limited, breeding may be difficult or impossible. Some captive-bred fish are of lower quality than wild-caught fish.

3) Use reverse osmosis water and add the appropriate minerals.
This method is used by fishkeepers with more sensitive livestock, i.e. marine fish, discus, Rift valley cichlids. RO water is either bought from a supplier or a RO unit can be bought to produce your own RO water. Then minerals are added to mimic the natural environment of the fish.
Advantages- You can match the exact requirements of your fish, making them healthier, happy and more likely to breed. You have a greater control over the water parameters.
Disadvantages- It can be very costly and inconvenient. You also need to have storage space for the RO water. Since buffers and other minerals are not present in RO water they must be added. Mixtures for various fish can be bought commercially.

Increasing hardness is normally fairly easy. Hardening materials such as crushed coral shell in the filter will gradually and nauturally raise KH and in turn pH. There are also commercially available hardening salts - these are often used for tanks containing cichlids from the African rift lakes, which are hard and alkaline.

One of the easier ways of increasing KH is to simply add a little Bicarbonate of Soda. Do not confuse this with Baking Soda though as this has additives in it which are not safe for tanks. Only a very small amount - think tip of a teaspoon, to begin with - is needed and as when altering any water pH levels, this needs to be undertaken very gradually. Running tests first is required to ensure you don't over treat. Post on the forum for specifics as this will depend on tank size and current readings.

Decreasing hardness can be done in two main ways: dilution with softer water, or adsorption of hardening ions. Some people use reverse osmosis (RO), distilled or deionised water (DI) to dilute their tap-water to a hardness suitable for their fish. Note that hardness has a fairly straight-forward relationship with dilution. For example, if your tap-water has a GH of 10 and you use half tap-water and half pure water, the GH will be 5. Pure RO cannot be used without prior re-mineralisation - see above.

Testing GH API test kits are commonly used for this. If so, the oDegrees of Hardness equate to how many drops of tester solution are needed to read the results. Fill the test tube up with 5mls of tank water. Add drops (1 by one, shaken). The test is completed when the water in the test tube, after having been shaken, turns from orange to green - count the drops - each drop is equal to 1 degree dGH or 17.9 ppm GH.

For example, if it takes 3 drops of reactant to change the test tube from orange to green that = soft water. 15 drops would mean moderately hard etc.

Testing KH Do the same for the API KH test. The carbonate hardness value is determined by the number of drops of the reagent that must be added to turn the water from blue to yellow. Each drop is equal to 1 degree dKH or 17.9 ppm KH.

GH Table:

mg/l CaC03 / oDegrees of Hardness / Described as:
0 - 50       /  0 - 3    / soft
50 - 100    /   3 - 6   / fairly soft
100 - 200   /  6 - 12  / slightly hard
200 - 300  /   12 - 18 / moderately hard
300 - 540  /  18 - 30 / hard
540 plus    /   30 plus / very hard
All articles are the copyright of their respective authors

Navigate through the articles
Previous article Culturing Daphnia Fishkeeping Tips and Things to Consider Next article
The comments are owned by the author. We aren't responsible for their content.
Author Thread