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. People can clean out an aquarium if it is dirty-looking. Aquarium water is actually made up of invisible waste chemicals that are derived from fish poop. These compounds can pose a danger if they are too high. 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

Test strips are the most common type of water test for fishkeepers. 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 can be very toxic to animals in high pH water. The recommended level should be 0 parts per million. It can be measured using the Ammonia Test Strips.

Aquarium Co-Op Ammonia Test Strips

1. Nitrite In an older aquarium that has been cycled, beneficial bacteria eats the ammonia and makes nitrite. Nitrite can also be toxic to animals. It can cause severe burns to fish’s skin and gills. Keep it below 0 ppm. Use Multi-Test Strips to measure it. 2. Nitrate: In a mature aquarium, another type of beneficial bacteria consumes nitrite and produces nitrate, which is less toxic to fish. We recommend that nitrate levels are kept below 50 ppm as a rule. If you have aquarium plants, they consume nitrate as food, so we like to maintain at least 20 ppm nitrate to keep them healthy. It can be measured with Multi-Test Strips. Read our article on nitrate to find out more. 3. Chlorine: If your drinking water comes from a municipal water supply, then most likely it is disinfected with chlorine or chloramine to eliminate pathogens. These chemicals are deadly to animals and must be removed from the water supply. Multi-Test Strips can be used to measure chlorine levels.

Aquarium Co-Op Multi-Test Strips

1. pH: pH tells you how acidic or basic the water is. The pH range of most freshwater fish is between 6.5 and 8.0. However, some species prefer a lower or higher pH. Measure it with Multi-Test Strips or the API High Range pH Test Kit.

API pH Test with High Range

1. GH General Hardness (GH) is a measure of how hard or soft water is. It is measured in either dGH (degrees GH) and ppm. We recommend that freshwater aquariums have between 4-8 dGH (or 70 to 140 ppm) of mineral content. 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. Like GH, it is measured in dKH (degrees of KH) or ppm, and we recommend keeping it at 3 dKH (50 ppm) or above for most freshwater aquariums to prevent pH swings. It can be measured with Multi-Test Strips, or the API GH & H 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. While every aquarium has its own fish and plant stocks, there are guidelines. Some hobbyists suggest 0.5-2ppm phosphate in low light tanks, and 3ppm or more in high light aquariums with CO2 injection. The API Phosphate Test Kit can measure it.

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 The Dennerle CO2 Quick Test can be used to determine the amount of dissolved CO2 in an aquarium. 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 and when to test aquarium water

Although water should be tested regularly, it is best to do so as frequently as possible. In the past, however, tests were costly and difficult to use. Fish keepers might overlook something unusual in their tanks and not test the water. 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. A new aquarium After setting up a fish tank, it is important to cycle the tank regularly to allow the biological filtration to mature enough to filter out your fish’s toxic waste. While the aquarium is cycling, it is important to frequently test the water on a daily basis to make sure the ammonia, nitrite, and nitrate levels do not get too high, so get the Ammonia Test Strips and Multi-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. Read our complete article to learn more about the aquarium cycle.

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 reading is higher than 50 ppm or lower, then it’s time to change your water. One of the main reasons we keep live plants within our aquariums is to help reduce the need for water changes. To find out the frequency of water changes based upon nitrate readings, please refer to our water chart flow chart.

1. Hungry Fish If you notice signs of illness in your pets, or if they are not eating properly, it is time to examine every parameter to diagnose the problem. Begin by checking the water temperature and multi-test strips. Use the API High Range Acid pH Test Kit if you suspect an abnormal rise in pH. Invertebrates like shrimp and snails are more susceptible to copper, so if you notice changes in their health, check your water with the API Copper Test Kit. It is important to determine whether the measured values are within a safe range and to also evaluate if they are significantly different from what you have previously seen.

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. Multi-Test Strips can be used to determine the level of nitrate in the aquarium. Keep it at 25-50ppm. 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. An overabundance or shortage in phosphate can cause problems like algae or leaves with large holes, so use the API Phosphate Test Kit to see what’s going on. 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. Outside Pond Large outdoor ponds with large amounts of water are best tested using the Ammonia Testing Strips and Multi-Test Strips at least three-to-four times per year. At the beginning of summer, we want to see how the water fared over the winter. You should check the water quality during the middle of the season, as the fish have been eating different food. Also, the pond will evaporate faster in 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. In order to keep track of water parameter values over time, many hobbyists mark them down in a journal or computer 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!