Testing Fish Tank Water: 4 Best Kits and How to Use Them

When starting up a fish tank, learning how to accurately test the water in the tank is one of the most vital skills necessary for keeping aquarium fish healthy. Aquariums are an enclosed system, so if there is any kind of chemical imbalance it can negatively impact every animal that lives in them. 

So how do you test fish tank water? There are many water testing kits (both freshwater and saltwater) available to test the levels of toxic chemicals in fish tank water, as well as the pH. These kits allow aquarium keepers to monitor for dangerous waste products such as ammonia, nitrites, nitrates, chlorine and chloramine that can sicken and kill fish. 

Testing fish tank water isn’t difficult, and once you know how to do it, you’ll be able to keep your aquarium pristine and your fish in good health. Read on to find out more about testing fish tank water and the best kits for the job. 

Why Water Testing in Fish Tanks is Important

If you’re new to keeping aquariums, you might not realize why testing the water in fish tanks is so crucial to keeping them in a good working condition. Here are some of the reasons why it’s so important for you to get your water tested on a regular basis: 

  • You don’t know what your baseline water looks like. Whether you get your water from a well or from a municipal water source so-called tap water, you don’t know how hard or soft the water is. Many tropical fish can only live comfortably within a tight pH range, and if you put soft water fish in a hard water tank, they aren’t likely to survive very long (and vice versa). This is especially true for more sensitive species such as discus.
  • Waste products build up in an aquarium gradually. Even if you keep your aquarium clean, ammonia and nitrates will build up quickly in a fish tank just from the waste (fish poop) of the animals in the tank. A very small percentage of waste ammonia per gallon is enough to sicken and kill your fish. The more fish you have stocked in your fish tank, the more quickly waste builds up.
  • Water testing is especially important in new tanks. In new tanks, beneficial bacteria isn’t very well established yet, which means that there can be spikes in ammonia or other dangerous waste chemicals if fish are added to a new tank too quickly for the beneficial bacteria to keep up. Regular water testing prevents fish die-offs or health problems related to bad water quality.
  • Different species have different needs for water quality. Some species of fish are very sensitive to poor water quality and can die quickly in a dirty aquarium, while others are hardier and forgiving to novice aquarists. Regardless of what species you keep, making weekly or monthly water testing a part of your regular aquarium maintenance can help you stay on top of things.
  • “Old tank syndrome” means it is still important to test older tanks too. Old tank syndrome is when nitrates build up in a tank over time. Nitrates cannot be filtered out of aquarium water by a filter and need to be removed manually via regular water changes. If nitrates are not removed by water changes and monitored by water testing, they can lead to severe health problems even in an established tank. 

No matter whether you’re just starting up a new aquarium or you’re trying to get an older one in good shape, water testing is one of the most important things you can do to get a handle on what your aquarium water quality is like and how you can improve it. 

How Should You Test Fish Tank Water?  

The easiest way to test aquarium water is through using an aquarium water testing kit. These kits are designed for either freshwater or saltwater applications and measure the following water quality levels: 

  • pH levels
  • Ammonia
  • Nitrites
  • Nitrates
  • Chlorine and chloramine
  • Water hardness

How often fish tank water should be tested is a matter of some debate among aquarists. If you are starting a new aquarium you should test the water every few days to see where the tank is in the nitrogen cycle, as this will determine when you can safely add fish to your setup. 

If your tank has been established for a few months, however, it is okay to only test your water once every few weeks or once a month just to keep an eye on things. As long as regular water changes are being performed, the quality of the water should remain fairly stable as long as the nitrogen cycle has already been established.

How to Test Fish Tank Water for Disease

The one thing that water testing kits cannot easily test for is disease in the water. Instead, if you suspect disease in your tank, this often must be diagnosed through direct observation of the fish themselves and how they look/act. 

If you suspect an epidemic outbreak of disease in your tank and cannot determine the symptoms, dead fish can sometimes be sent away to labs for testing to determine their cause of death. The cost for this can vary depending on where the fish is sent. However, this is not usually undertaken unless there is a serious illness suspected that would require the entire tank to be euthanized, such as tuberculosis.

Rather than testing for disease in your fish tank, it is much easier to prevent disease from occurring in the first place. Here are some methods you can use to prevent an outbreak of disease in your tank: 

  • Set up a quarantine tank. A quarantine tank is one of the best preventative measures to keep diseases from being introduced to your aquarium through the introduction of new fish. Putting new fish in a quarantine tank for two weeks before introducing them into your main tank can allow you to observe any signs of disease or parasites in a fish before they can pass them on.
  • Observe your fish. It’s a good idea when you have an aquarium to set aside a few minutes a day to simply observe each individual fish carefully and take notes of their behavior or appearance. Catching a disease in one fish early can allow you to quarantine the fish before that disease can be passed to others since many fish diseases are communicable diseases.
  • Regular water changes deter disease. Since disease cannot be monitored through most standard water testing kits for aquariums, it’s important to take measures to prevent disease from being introduced or spreading in a tank. Replacing 10-25% of the water in an aquarium once a week can not only keep your tank sparkling clean, it can help prevent illness too.
  • Think about using ultraviolet filters. There are many filters available now that pass water through UV light exposure that kills many viruses and bacteria that can sicken fish and reduce fish tank water quality. 

Testing for disease with water testing kits can be tricky, so it’s important to keep an eye on your tank outside of water testing to keep your fish tank in good working order. 

How to Test Fish Tank Water for Quality

The most important aspects of aquarium water to test determine its overall quality are pH, ammonia, nitrites, and nitrates. These are the water quality factors that are most likely to negatively impact an aquarium’s ecosystem and cause illness in your fish. 

Here is what you can expect to find if you purchase an aquarium water testing kit: 

  • Instruction manual: This part of your water testing kit will explain exactly how to use it, so be sure not to throw it out! Each testing kit is slightly different so it’s important to read the directions thoroughly before attempting a water test to ensure accurate results.
  • Test tube(s): The test tube is the part of the water testing kit used to collect the water sample from your aquarium.
  • Testing chemicals: The testing chemicals in the water testing kit are combined with aquarium water to determine various quality measures such as pH or ammonia. It is important to handle fish tank water testing chemicals carefully, as many of them can be caustic and burn the skin or eyes if exposed.
  • Reference card: A color-coded reference card is included with water testing kits so that you can use the colors to determine water quality based on the outcome of the chemical test. 

Once you have your water testing kit, use the following procedure to start a water test: 

  • #Step 1: Take a sample of your aquarium’s water in the test tube.
  • #Step 2: Add testing solution for the parameter you’re checking. Your testing chemicals will be labeled with the parameter they are intended to measure such as ammonia, pH, etc…
  • #Step 3: Shake the test tube dosed with testing chemicals gently to make sure that the chemicals are evenly distributed throughout the water sample.
  • #Step 4:Check the color of the test water against the color-coded reference card to determine your water quality. 

This method can be used to test most major water quality parameters that could negatively impact the closed ecosystem of an aquarium. 

If testing determines that you have high levels of ammonia or nitrates in your water, the best thing to do is to begin a daily regimen of replacing 10% of the water a day with clean, dechlorinated water that has been brought to approximately the same temperature as the water in the aquarium. This is preferable to doing large water changes on the tank, as this can be just as stressful to the fish as bad water quality.

Whenever you make adjustments to parameters of the water in your aquarium, it’s important to do so gradually so that the fish don’t become shocked by a sudden change in their environment. 

Some fish are more sensitive than others and introducing large quantities of new water into an established tank can not only throw off the nitrogen cycle and cause an ammonia spike, the pH shock can cause serious problems. 

How to Test Fish Tank Water for Hardness

One of the water qualities that most standard testing kits look for is water hardness, which determines how many dissolved minerals your water has in it. Fortunately, most store-raised tropical fish have become very adaptable to varying levels of water hardness and can tolerate it quite well. However, there are some types of tropical fish (such as discus or other wild-caught species) that are sensitive to it.

Once you’ve tested your water and determined its hardness, there are a few different ways you can adjust the hardness of the water to suit the fish you’re trying to keep. Water can be softened with additives such as peat or driftwood, while it can be hardened by using materials such as crushed coral substrate, fish tank limestone or even oyster shell. 

It is important not to shift any aquarium water parameter too quickly, as any major changes performed at once can be just as stressful to the fish as doing nothing at all. 

4 Best Kits for Fish Tank Water Testing

Ask most experienced aquarium keepers what their preferred water testing kit is, and you’re probably going to hear a lot of references to API Master Test Kits. These kits are some of the most comprehensive and easy-to-read tests that are available to not only beginning aquarists, and they are widely distributed throughout most major pet supply stores such as PetSmart or Petco. Test kits are also available online on Amazon.

Here are four of the best test kits you can find for testing your fish tank water: 

  • API Freshwater Master Kit: This is an aquarium kit that is designed to test water in freshwater aquariums and can test for ammonia, nitrite, nitrate, and pH.
  • API Saltwater Master Kit: This is an aquarium kit that is designed to test water in saltwater aquariums and can test for ammonia, nitrite, nitrate, and pH (high range).
  • API Reef Master Kit: This is a more advanced water testing kit for those aquarists who have reef animals such as coral that require more chemical fine-tuning than your average freshwater aquarium. These test kits test for calcium, KH, phosphate, and nitrate.
  • API 5 in 1 Pond Test Strips: This is a kit that is designed to test pond water and as such it has a stronger emphasis on phosphate testing, which is important to deter the overgrowth of algae in an outdoor tank or water feature. 

Each of these water testing kits is especially calibrated to check the parameters that are most important in the type of aquarium they’re designed for. For example, someone running a reef tank is going to be more concerned with calcium levels than someone running a basic freshwater tank, and someone who has a pond full of koi fish will need to test for different things than someone who has a saltwater nano tank.

Benefits of Keeping a Water Testing Kit on Hand

There are many benefits to keeping one of these test kits on hand at all times even if you’re not establishing a new aquarium. Here are some of the reasons that it’s important you should have a water testing kit whether your tank is already set up or not: 

  • Testing prevents fish illness and death. Unless you test your water regularly, the first indication that you’ll get that the water is going bad is that your fish will start to get sick or die. If you’re emotionally invested in your fish as pets or have spent money on expensive tropical fish, you don’t want their sudden death to be your first indication that something has gone wrong.
  • You can test quickly if you notice a problem. If your fish starts to act strange, you can act more quickly to troubleshoot and rectify the problem if you’re able to test your aquarium on the spot rather than go out looking for a test kit whenever a problem occurs. The sooner you can identify the issue, the less chance there is that you will lose fish in the process.
  • Testing is crucial for maintaining saltwater tanks. Saltwater tropical fish are notoriously more delicate than freshwater fish and more susceptible to death if parameters are off, so if you have a saltwater tank, testing is especially important. For saltwater tanks fresh sea water has to be created each time a water change is made, so maintaining stable water parameters is important.

Since water testing kits are relatively inexpensive and most of them can last years before expiration, they are a worthy investment for anyone who is considering getting into the aquarium hobby, or anyone who is trying to become more seriously invested in the tank or tanks they already have. 

Water Testing Kits Are Important for All Aquariums

Whether you’ve had your aquarium for years or you’re just getting one started up, testing the water regularly to determine parameters for ammonia, pH, and other issues can be the difference between losing a bunch of fish and having a healthy, vibrant tank. 

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