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”. Aquarium water can contain invisible waste chemicals, such as fish poop, and other compounds that could be harmful at dangerous levels. The only way to determine if your aquarium water is safe and clean enough for plants and fish to drink is with test kits.

How to Test 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. The chemical reagent is added to a sample of aquarium waters and the color changes according to the water parameter being tested. After a time period, the reagent can be compared to a chart to show the final results. Here are the most common parameters we recommend looking at:

1. ammonia: ammonia is made by your fish or invertebrates using their waste. It is very toxic to animals, especially in water with high pH, and should stay at 0 ppm (parts per million). Measure it with the Ammonia Test Strips.

Aquarium Co-Op Ammonia Test Strips

1. Nitrite: In a mature aquarium that is cycled, beneficial bacteria consumes the ammonia and produces nitrite. Nitrite is toxic to animals. It can burn fish skin and gills. Multi-Test Strips can be used to measure it. 2. Nitrate A mature aquarium will have another type of beneficial bacteria that consumes nitrite to produce nitrate. This is less toxic for fish. As a general rule, we recommend keeping nitrate at 50 ppm or below. Aquarium plants eat nitrate, so we recommend keeping it below 20ppm to ensure their health. To find out more, use Multi-Test Strips to measure it. 3. Chlorine Drinking water from municipal water supplies is most likely disinfected with chlorine and chloramine to kill 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 is a way to tell how acidic or base the water. 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: The General Hardness (GH), which measures how hard or hard water is, is measured either in dGH or 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. KH: Carbonate hardness (KH) measures the buffering capacity of the water. The higher the KH, the less likely the pH will rapidly change, which can be dangerous to fish. It can be measured in dKH, or degrees of KH, just like GH. We recommend keeping it below 3 dKH (50 ppm), for freshwater aquariums. This will prevent any pH swings. It can be measured with Multi-Test Strips, or the API GH & H Test Kit Combo.

API H & KH Testing Kit Combo

1. Phosphate –Phosphate, a macronutrient, is what plants need to grow well. However, excessive phosphate can lead to algae growth and damage fish health if it is too high. 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. The API Copper Test Kit can be used to determine the level of copper in tap water and to prescribe the right amount of copper-based medicine for sick fish.

API Copper Test Kit

1. CO2: If you are setting up a DIY or pressurized CO2 system, the Dennerle CO2 Quick Test is an easy and accurate way to measure the dissolved CO2 in your aquarium. To determine if your tank has enough CO2, fill the test tube half way with water. Then, shake the tube for a while and compare it to the chart.

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. Aquarium Co-Op test kits were created to be easier and less expensive so that you can test more often to ensure your peace of mind. Here are the most common circumstances in which we recommend testing 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. You can read the full article about aquarium cycles.

1. Tank Maintenance After your aquarium has been cycled, you will only need to use the Multi Test Strips once every 2 weeks to check for nitrate levels. Nitrate can be toxic at extremely 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. Live plants are essential for aquariums. They help to reduce the amount of water changes needed by consuming nitrate. You can use our water chart flow diagram to determine how often water changes should be made based on your nitrate reading.

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. Check the water temperature, pH, Multi-Test Strips, as well as Ammonia Test Strips. The API High Range pH Testing Kit can be used to detect abnormal pH changes. Copper is more toxic to invertebrates such as shrimps and snails. If you suspect that your water has changed, the API Copper Test Kit will help you test it. 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 can be affected by sudden or abnormal changes in the 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 nitrate is below this amount, then it may be time to dose some Easy Green all-in-one fertilizer to replenish the 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. If you want to increase plant growth by adding CO2 gas, the Dennerle Co2 Quick Test will help you find out how much CO2 is present in the aquarium.

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. The water quality should be checked at the beginning of each season to determine how it has fared in the winter. Check the water quality in the middle of summer. The fish have been eating different foods and the pond evaporates more quickly during 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. Many hobbyists keep track of water parameters over time by keeping them in a notebook or 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!