How (and How Often) to Test Aquarium Water for Healthy Fish and Plants

Regular water testing is vital for keeping tabs on the health of your aquarium fish and plants, but most beginners in the fishkeeping hobby are not aware of the importance of this practice. The aquarium may need to be cleaned if it looks “dirty”. In reality, aquarium water contains invisible waste chemicals from the fish’s poop and other compounds that can be dangerous at high enough levels. Test kits are the only way to accurately measure if your water is clean and safe enough for fish and plants to live in.

How to test the water in a fish tank

The most readily available types of water tests for fishkeepers are (1) test strips and (2) test kits that come with test tubes or other small containers. Mixing a small amount of aquarium water with chemical reagent will change the color depending on the water parameter being measured. After a time period, the reagent can be compared to a chart to show the final results. These are the most important parameters that we recommend you look at:

1. Ammonia: Ammonia is produced by your fish and invertebrates from their waste. It is very toxic to animals, especially in water with high pH, and should stay at 0 ppm (parts per million). Use the Ammonia Testing Strips to measure it.

Aquarium Co-Op Ammonia Test Strips

1. Nitrite When an aquarium is mature and cycled, beneficial bacteria consumes ammonia to make nitrite. Nitrite is toxic to animals. It can burn fish skin and gills. Multi-Test Strips can be used to measure it. 2. Nitrate Another type of beneficial bacteria will consume nitrite in mature aquariums and produce nitrate which is more toxic to fish. As a rule of thumb, we recommend that the nitrate level is kept at 50 ppm. Aquarium plants eat nitrate, so we recommend keeping it below 20ppm to ensure their health. Measure it with Multi-Test Strips, and read our nitrate article to learn more. 3. Chlorine Drinking water from municipal water supplies is most likely disinfected with chlorine and chloramine to kill pathogens. These same chemicals are lethal to animals, so a dechlorinator must be used to make the tap water safe. Multi-Test Strips are used to test for chlorine.

Aquarium Co-Op Multi-Test Strips

1. pH: pH tells you how acidic or basic the water is. While most freshwater fish can survive at pH levels of 6.5 to 8.2, some species prefer pH levels that are lower or higher. You can measure it using Multi-Test Strips and the API High Range pH Testing Kit.

API Higher Range pH Test

1. GH: General hardness (GH) describes how hard or soft the water is, and it is measured in dGH (degrees of GH) or ppm. For freshwater aquariums, we recommend that you keep between 4-8 and 70-140ppm of minerals. You can measure it using Multi-Test Strips, or the API GH & H Test Kit Combo. 2. H: The water’s buffering capacity is measured by carbonate hardness (KH). The higher the KH, the less likely the pH will rapidly change, which can be dangerous to fish. It is measured in dKH or ppm (degrees of KH), and for freshwater aquariums, we recommend that it be kept at least 3 dKH or 50 ppm to avoid pH swings. You can measure it using Multi-Test Strips and the API GH &KH Test Kit Combo.

API-GH & H Test Kit Combo

1. Phosphate: Phosphate is a macronutrient that plants need in order to grow well, but excess phosphate can cause algae growth and even harm fish health at high enough levels. Each aquarium is different and each fish and plant stocking levels are different. However, hobbyists recommend a minimum of 0.5-2 ppm for low-light tanks and 3 ppm for high-light aquariums that use CO2 injection. Measure it with the API Phosphate Test Kit.

API Phosphate Test Kit

1. Copper: The copper-containing medications used to treat fish diseases may contain copper. Use the API Copper Test Kit to measure the presence of copper in your tap water or to dose the correct amount of copper-based medication for sick fish.

API Copper Test Kit

1. CO2 This quick test is for measuring the dissolved CO2 content in your aquarium. It can be used either to set up a DIY system or pressurized CO2 systems. Fill the prepared test tube halfway with tank water, shake for a few seconds, and immediately compare it to the color chart to see if you have too little, too much, or just the right amount of CO2.

Dennerle CO2 Quick Test

How often and when should you test your aquarium water?

Ideally, water should be tested as often as possible, but in the past, test kits were often time-consuming and cost prohibitive to use very often. These obstacles can lead to fish keepers ignoring any unusual behavior in their tanks or avoiding testing it. Therefore, we developed the Aquarium Co-Op test strips to be faster and cheaper to use so that you can test more frequently for peace of mind. These are some of the most common situations in which you should test your water.

1. New Aquarium When setting up a new fish tank, it takes a while to cycle the aquarium so that the biological filtration is mature enough to purify the water from your fish’s toxic waste. It is vital to test the water daily while the aquarium is being cycled. This will ensure that the levels of ammonia, nitrite and nitrate are not too high. You can get the Multi-Test Strips or Ammonia Test Strips. If the results are consistently safe and repeatable, you can decrease testing to every three days, then once a week, and eventually once a month. You can read the full article about aquarium cycles.

1. Tank maintenance You may not need the Multi-Test Strips for your aquarium after it has been cycled. This is because nitrate can cause toxic reactions at high levels. We try to keep the nitrate level below 50ppm. If the nitrate level is between 75 and 100 ppm, it’s time for a water change. One of the main reasons we keep live plants within our aquariums is to help reduce the need for water changes. You can use our water chart flow diagram to determine how often water changes should be made based on your nitrate reading.

1. Missing Fish If any of your animals show signs or are acting strangely, you should check all parameters to determine the cause. Start by checking the water temperature, Ammonia Test Strips, and Multi-Test Strips. Use the API High Range Acid pH Test Kit if you suspect an abnormal rise in pH. Copper is more dangerous to invertebrates, such as snails and shrimp. The API Copper Test Kit can help you check the water quality. It is crucial to assess if the results are within a healthy range, and also to see if they differ from previous readings.

Fish health problems can arise from sudden changes in water parameters.

1. Unhealthy Plants When balancing the lighting and nutrients in a planted aquarium, nitrate is a key component to keep an eye on. Use the Multi-Test Strips to measure the nitrate level and keep it between 25-50 ppm. If the nitrate level is lower than this, it might be time to add Easy Green all-in one fertilizer to replenish nutrients in the water. If there is an excess or a shortage of phosphate, it can cause algae growth or leaves with large holes. The API Phosphate Test Kit will help you determine the situation. Finally, if you are adding CO2 gas to the water to increase plant growth, get a read on how much dissolved CO2 is in the aquarium with the Dennerle CO2 Quick Test.

1. Outdoor Pond Large outdoor ponds that have large volumes of water should be tested at least three to five times per year with the Multi-Test Strips or Ammonia Test Strips. We want to check the water’s performance over the winter at the start of the summer. In the middle of the summer, check the water quality because the fish have been eating different kinds of food and the pond evaporates faster in the warmer weather.

At the end of pond season, make sure all the water parameters are safe before preparing for the cold weather. Finally, it may be good to do an extra test in the middle of winter to see how the fish are doing.

Water test kits can be used for both aquariums and outdoor ponds.

The more mature and problem-free a fish tank is, the less frequently we tend to test it, but don’t forget that your aquarium is a living ecosystem and things are constantly changing. You should test your aquarium again if you travel, change fish food, buy or sell fish, add or remove plants or make other changes to the tank. Hobbyists often keep track of water parameters by writing them down in a journal, or using a spreadsheet. For a fish room with multiple tanks, our CEO Cory will mark the results down on blue painter’s tape and stick it directly on the aquarium glass.

To learn more about water chemistry, we’ve gathered a series of articles to help you increase your knowledge and enjoyment of the fishkeeping hobby. Take a look at them and get out there enjoying nature everyday!