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The Basics Of Aquarium Water Chemistry Explained

Monitoring the chemistry of aquarium water and making changes when necessary is one of the many things you can do to keep your tank healthy and your aquarium fish thriving.


water xs 15891027The term “water chemistry” is used by aquarium hobbyists to describe the physical and chemical characteristics of the water in an aquarium. These characteristics typically include the pH, alkalinity, water hardness and salinity of the water as well as dissolved nutrients and chemicals. Water chemistry is very important in maintaining a healthy aquarium because unless you understand the basics of water chemistry and regularly test the water in your tank, you will be unequipped to keep the water quality in your tank high. If the water quality in your tank declines your fish could become stressed and, as a result, may become more susceptible to disease. Monitoring the water chemistry in your tank and making changes when necessary is one of the many things you can do to keep your tank healthy and your aquarium fish thriving.

How to Test Water Quality

tetraeasystripskitThankfully, testing the water quality in your aquarium has been made easy by the availability of aquarium water testing strips. You can find these strips, along with entire testing kits, at your local pet store and you can also order them online. Aquarium water testing kits come with a set of instructions as to how to use the enclosed materials. Most test kits are fairly simple to use, however, and follow the same basic principle. Some test kits come with paper strips that you dip into a cup of tank water and then compare the color on the strip to a chart included with the kit. Other kits require you to take individual samples of aquarium water then add a few drops of the test solution. Once the sample changes colors, it can then be compared to the chart included with the kit. It is wise to perform these tests on a weekly basis to prevent any sudden drops or spikes in water chemistry that could negatively affect your fish as well as the water quality in your tank. One company that’s made it fast and easy to test aquarium water is Tetra. Tetra Easy Strips provide 7 tests in one kit. Scientific quality results are ready in 60 seconds or less and there’s no solutions to mix – just dip and read. It can’t get any easier than that!

Components of Water Quality

pH – The pH in your tank is simply a measure of how acidic or alkaline the water is. PH is measured on a scale from 0 to 14 – a reading of 7.0 is considered neutral while readings above 7.0 are alkaline and below 7.0 are acidic. The proper pH for a freshwater aquarium depends on the particular species of fish being housed in the tank, but for a community tank housing a variety of tropical species, a pH of 7.2 to 7.8 is recommended. The pH in your tank should be tested on a weekly basis because organic materials such as fish waste and uneaten fish food can cause the pH level to change.

ph scale xs 15538980Buffering Capacity – This term is used to describe the ability of aquarium water to maintain a stable pH. As acids and bases are added to the aquarium, water that has sufficient buffering capacity should be able to absorb the acids, thus preventing any significant change in pH. Aquarium water can only provide so much buffering, however, so once the buffering capacity has been used up changes in pH can occur quickly if acids or bases are added. The most significant contribution buffering capacity makes to your aquarium is during the nitrogen cycle. During this cycle, nitrates (nitric acid) are produced which, if not for the buffering capacity of your aquarium water, would result in a gradual drop in pH. The buffering capacity of aquarium water is typically described in terms of KH (carbonate hardness or alkalinity) which can be measured in degrees of general hardness, or °dH.

General Hardness (GH) – Different from carbonate hardness (KH), general hardness measures the non-carbonate hardness of water. General hardness (GH) measures the concentration of dissolved ions such as calcium, magnesium and other minerals in aquarium water. When it comes to measuring the hardness of water, the terms “soft” and “hard” are often used. Soft water typically has a measurement between 0° and 3.36°dH, moderately hard water measures between 3.42° and 6.72°dH and hard water measures between 6.78° and 10.08°dH. Water that reads above 10.14°dH is said to be very hard. Frequent water changes are necessary in order to maintain a stable GH.

refractometerSalinity – The salinity of aquarium water is a measure of its salt content. The most common way to measure salinity is through the use of a hydrometer or refractometer. Specific gravity is another way to measure the amount of dissolved salts in aquarium water and it has a different scale than salinity. Salinity is measured in parts per thousand (ppt) whereas specific gravity is measured in terms of the ratio of the density of aquarium water to the density of pure water. The specific gravity of pure water is 1.0000g/cm3 – thus, water with any salt content at all will have a specific gravity above 1.0000.  

Nutrients and Trace Elements – One of the elements that should be tested for frequently in the home aquarium is ammonia (NH3). This substance is toxic to fish, so its levels need to be closely monitored with regular water tests. Nitrite and Nitrate levels should also be tested. Nitrites can prevent fish from breathing properly and high nitrate levels often indicate a build-up of fish waste and organic compounds which can negatively affect water quality. Electrolytes are molecular substances which are important for regulating hydration, blood pH, disease resistance and muscle function in fish. Calcium, Magnesium, Potassium and Sodium are some of the most important electrolytes which can be tested for.

Tips for Maintaining High Water Quality

The key to keeping your aquarium clean and your fish happy is to maintain high water quality. If the water in your tank is cloudy, dirty or contains high levels of toxins and dissolved waste your fish could become stressed. A stressed fish is more susceptible to disease and can deteriorate quickly if the cause for its stress is not remedied. In order to keep the water quality in your tank high it is essential that you perform regular water changes and monitor water quality with routine water tests. Small water changes between 10% and 20% should be made on a weekly basis and a larger water change, at least 25%, may need to be made once a month. These regular aquarium water changes will help to prevent the build-up of harmful toxins and other wastes that cause a drop in pH and negatively affect the overall quality of water. In turn, your fish will be much more healthy and happy and have a better chance of fighting off disease.

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