Water Chemistry

What is Water Chemistry and Why is it Important?


You have probably heard it said that maintaining stable water chemistry is the key to keeping your fish and your fish tank healthy. If you are unfamiliar with this term, however, you may find yourself asking “what is water chemistry?” Water chemistry is a term used to describe the chemical and physical characteristics of tank water. The characteristics of water quality may include the water hardness, the pH, the salinity level and the amount of dissolved chemicals in the water. All of these characteristics play a role in keeping your aquarium water clean and healthy for aquarium fish. If you do not understand the basics of water chemistry you will be ill equipped to make modifications when they become necessary, so do yourself a favour and brush up on the basics of aquarium chemistry.

Elements of Water Chemistry


The main component of water chemistry is pH. This is a measurement of how acidic or alkaline the water in your tank is. PH measurements range from 0 to 14 and readings above 7.0 are considered alkaline while readings below 7.0 are acidic. The proper pH for a freshwater tank depends on the type of fish you intend to keep. Some fish come from naturally acidic environments while others prefer a more neutral pH. Before you add any fish to your aquarium, do some basic research to see what pH your fish prefer. Another element of water chemistry that is related to pH is the buffering capacity. Buffering capacity is a term used to describe the ability of tank water to keep the pH stable. Tank water that has a healthy buffering capacity should be able to prevent any major changes in pH as acids or bases are added to the tank through substrate, medications or other additives.


The general hardness of aquarium water is a measurement of the concentrated dissolved ions in tank water. The ions general hardness measures for generally include calcium, magnesium and several others. In describing the general hardness of aquarium water, hobbyists use the terms “hard” and “soft” and the actual measurements are taken in degrees of general hardness, or °gH. While it does not generally apply to freshwater tanks, the salinity level or specific gravity of tank water is also a component of water chemistry. While salinity is more important in saltwater tanks, some freshwater fish like the puffer fish prefer some degree of salt in their water. Salinity can be measured using a hydrometer or refractometer. The final component of water chemistry involves dissolved ions and chemicals. Some of the most common elements found in aquarium water include ammonia, nitrite and nitrate. In order to keep your tank healthy, the levels of these elements must be controlled.

Importance of Water Chemistry


Maintaining stable water chemistry in your tank is not only essential to keeping your aquarium water clean and clear, it is also important for the health of your fish. While some species of fish are capable of adapting to slight changes in water chemistry, other species are very sensitive and could die if the water chemistry changes suddenly. Even if your fish do not die immediately as a result of changes in water chemistry, their health could decline slowly over time. If the water quality in your tank declines, your fish could become stressed and may become more susceptible to illness. In order to prevent this from happening, keep a close eye on your water chemistry and perform routine water changes to keep it stable.


How Do I Monitor and Modify the Water Parameters in my Tank?

 Monitoring and keeping the water chemistry in your tank stable are some of the most important tasks you must do as an aquarium hobbyist. Water quality correlates directly to the health of your fish – if the water quality in your tank is poor, your fish may become stressed and their health may decline. On the other hand, if you keep the water in your tank clean and the water parameters stable your fish will likely be healthier and less susceptible to disease. In order to keep the water chemistry in your tank stable you need to know how to measure it and, once you have done so, you must be capable of making corrections when necessary. Fortunately, monitoring your aquarium water chemistry requires nothing more than a simple aquarium water test kit.


 Monitoring Tank Parameters


You can find a basic aquarium water test kit either online or at your local pet store, usually for around $15 to $20. There are several different kinds of kits but two of the easiest to use are those that utilize paper test strips and test tube samples. To use a water test kit featuring paper test strips all you have to do is dip the test strip into a cup of aquarium water. Once the paper has soaked up the water, compare the colour of the sample to the colour chart included with the kit. Test tube sample kits may require a little more time to use but they are just as easy. Simply collect samples of your aquarium water in the test tubes provided with the kit and squeeze in a few drops of the testing solution. Then, just as you would with a paper test strip kit, compare the colour of the sample to the colour chart included with the kit. It is wise to test your aquarium water on a weekly basis and to record the results in a notebook so you can form an understanding of what is “normal” for your tank and so you can catch any changes in water chemistry before they become drastic and affect your fish.


Modifying Water Chemistry

If you maintain your tank properly by performing routine water changes you should not have any major problems with water chemistry. Accidents do happen, however, and in the event that your tank goes through a change in water chemistry it is wise to equip yourself with the knowledge to remedy the situation. If the pH in your tank falls below its normal level there are several things you can do. Adding 1 teaspoon of baking soda per 10 gallons of water in the tank should raise the pH. If you need to increase both the pH and the hardness in your tank, combine equal parts Epsom salt, baking soda and calcium chloride then add 1 teaspoon of this mixture for every 5 gallons of tank water.

Lowering the pH in your tank can be more difficult than raising it unless you are able to lower the buffering capacity of the water at the same time. Buffering capacity is the ability of water to maintain a stable pH. Thus, if you try to lower the pH in your tank without also buffering it to a pH, your efforts may be ineffective or the result could be an unnaturally low or unstable pH. To lower the pH in your tank you first need to add some naturally soft water – rainwater or melted snow are good sources of naturally soft water. Then, you can begin lowering the pH in your tank by adding peat moss or injecting CO2.


The hardness of the water is the other aspect of water chemistry that you may occasionally need to alter and increasing the hardness is much easier than lowering it. To increase water hardness, simply add 1 teaspoon of Epsom salt per 10 gallons of aquarium water. If you don’t have Epsom salt, adding calcium carbonate or marine salt can also harden the water. If you often have trouble with your tank water being too soft, consider utilising calcitic gravel as the substrate in your tank. If you choose to do this, however, you should be aware that it could also raise the pH in your tank up to 7.5. To soften the water in your tank it is best to start with water that is naturally soft like rainwater or melted snow. If these options are not available, you may use a reverse osmosis unit or purchase distilled water for your tank.