Testing aquarium or pond water is both a critical and essential step in maintaining a healthy, thriving aquatic environment. It allows hobbyists to monitor and maintain the water parameters necessary for the well-being of all fish, plants, and other inhabitants within.

One of the main reasons to test water is to ensure that the chemical composition of the water is in correct balance. This includes parameters such as ammonia, nitrite, nitrate and pH levels. By regularly testing these parameters, fishkeepers can quickly identify any potential issues and take appropriate measures to correct them before they have a detrimental impact on the aquarium or pond inhabitants. By doing so, this also helps to prevent outbreaks of diseases and other health issues. For example, high levels of ammonia or nitrite can be toxic to fish, causing stress and making them more susceptible to diseases. Regular testing allows fishkeepers to detect and address these issues promptly, minimising the risk to the inhabitants of an aquarium or pond.

In addition, testing water is essential for monitoring the effectiveness of the filtration and maintenance processes. By regularly testing the water, hobbyists can ensure that the filtration system is functioning as it should and that regular water changes are maintaining a healthy environment for the aquarium inhabitants.

Testing your source water


If you use tap, borehole, water-butt or well water testing this source water is also an important step in ensuring the health and safety of any fish, .plants and invertebrates in your care. When considering testing the source water, its essential to focus on key parameters that can directly impact the aquatic environment. These parameters include (but are not limited to) pH, ammonia, nitrite, nitrates and chlorine/chloramine levels

Some of these substances can occur in your source water for numerous reasons (eg agricultural run-off or other environmental factors). Tap water will invariably contain chlorine or chloramine, which are introduced into the water to kill bacteria. However, these chemicals can be harmful to both aquatic life and filter bacteria. 

Testing for such parameters helps you assess the initial water quality and make informed decisions about the need to fins an alternative source, such as reverse osmosis (RO) water. Testing source water is an essential practice for responsible fishkeeping maintenance and contributes to the overall health and longevity of the aquatic ecosystem you are caring for. 

Reverse osmosis (RO) water


Reverse osmosis water is a type of purified water that has undergone a filtration process. Water is passed through a semi-permeable membrane to remove impurities, contaminants, and minerals, resulting in highly purified water. These impurities may include dissolved solids minerals, salts, chemicals, heavy metals and other contaminants present in the source water. 

As a result, RO water is known for its purity, as it is free from many of the substances found in regular source water. This makes it an ideal choice for fishkeeping, being a clean and consistent water source for fish and other aquatic life. Because it is essentially devoid of dissolved solids and impurities, it serves as a blank canvas for aquarium hobbyists to create specific water conditions suitable for different species of fish and aquatic plants. 

It’s important to note that while RO water is highly pure, it is also devoid of essential minerals that may be beneficial to aquarium inhabitants. As a result aquarium hobbyists often use remineralisation to add back necessary minerals and achieve the ideal water chemistry for their specific aquatic set-ups.

Most Common Tests

Ammonia (NH3): A primary waste product, ammonia is highly toxic and should be zero in a properly managed aquarium or pond. The presence of ammonia indicates a breakdown in the balance between waste levels and filter bacteria – no livestock should be added to a system which tests positive for its presence. In acidic water, ammonia becomes a less toxic form – ammonium. Ammonia is measured in ppm (parts per million). 

Nitrite (NO2): The result of ammonia decomposition, nitrite is also harmful and should be zero in a properly managed aquarium or pond. The presence of nitrite indicates a breakdown in the balance between waste levels and filter bacteria – no livestock should be added to a system which tests positive for its presence. Nitrite is measured in ppm (parts per million). 

Nitrate (NO3): The least toxic of the nitrogen-based pollutants, nitrate is less harmful but can be problematic if allowed to accumulate. Aim to keep levels as low as possible and certainly less than 40ppm. Be aware that established livestock can adapt to higher concentrations that will be harmful to newly added animals, even members of the same species. Nitrate is measured in ppm (parts per million). 

KH (carbonate hardness): A measure of the biologically available minerals, carbonate hardness buffers organic acids that would otherwise drop pH levels, as well as being important for the healthy metabolic function of aquatic creatures including filter bacteria. Ideal range will vary depending on the species kept but most aquaria should be kept within a range of between 6 and 15dKH. For a pond, levels should be between 6 to 14dKH. KH is usually measured in degrees of hardness (1 dKH is equal to 17.9mg/l or 17.9ppm).

GH (General hardness): Unlike KH, general hardness doesn’t fluctuate and has less of a bearing on the day-to-day running of an aquarium or pond. GH and KH aren’t always closely related and it may be necessary to buffer a low KH despite high GH values when keeping hard-water species. In general, a GH level of between 4 and 8 dGH is acceptable an aquarium, 8 and 12 dGH in a pond. GH is usually measured in degrees of hardness (1 dGH is equal to 17.9mg/l or 17.9ppm).

pH: Measures the acidity or alkalinity of water. pH can be very significant for species adapted to extreme conditions and for these, some manipulation may be required, often in tandem with adjustment of KH as the two parameters are closely linked. For most aquarium and pond species a pH around neutral (7 – 7.5) is ideal but tap water often carries values of 8 or above, which may be too high for softwater species. Before attempting to lower pH, the KH usually has to be lowered and dilution with purified water is the best way to accomplish this. Take care if altering pH and ensure KH values are high enough to prevent a crash into levels which can cause acidosis. pH is a logarithmic scale, meaning that an increase or decrease of an integer value changes the concentration by a tenfold. For example, a pH of 5.5 is ten times more acidic than a pH of 6.5. pH has a range from 0 (acidic) to 14 (alkaline).

Temperature: A parameter which can shift far more rapidly than any other, water temperature has a significant impact on the health of our cold-blooded pets. For some aquarium species, fluctuations are a natural part of daily or seasonal cycles, whereas others come from habitats that show a good deal of stability and can be stressed by values outside of an optimal bracket (e.g a reef aquarium). Temperature can be measured in either Fahrenheit (°F) or Celsius (°C).

Phosphate (PO4): A waste product that can fuel nuisance algae growth if allowed to accumulate, phosphate can also prove harmful to delicate invertebrates and fish. Trace amounts are needed for desirable plants and algae, but high concentrations can lead to mortality in sensitive species and ailments such as lateral line erosion in more robust fishes. Ideally, phosphate levels should be between 0.02 and 0.10 in freshwater aquariums and ponds, and between 0.01 and 0.03 in marine aquariums. Phosphate is measured in ppm (parts per million)

Specific Gravity: In the context of aquarium keeping, specific gravity or SG is a measure of salt content and has a bearing on the health of marine and brackish creatures. As with a few other parameters, fluctuations are either best avoided in the case of marine invertebrates or encouraged when keeping estuarine animals that originate from tidally influenced habitats. Best measured with a refractometer with a recommended range is between 1.022 to 1.028 (salinity of 29 to 37ppt). Specific gravity is the ratio of a material's density with that of pure water at 4 °C and therefore a relative quantity with no units.

Calcium (Ca): A very important element for the growth of coral skeletons, calcium can be quickly depleted by fast-growing corals and low levels will restrict health and vigour. High levels can affect pH and are best avoided. An optimal calcium range in a reef aquarium is 350 to 450 which is vital for coral calcification and skeletal formation. Calcium is measured in ppm (parts per million).

Magnesium (Mg): Together with calcium, magnesium is an important component of healthy coral skeletal growth. Low magnesium levels can inhibit calcium uptake, and the two parameters should be monitored closely in systems housing fast growing SPS corals especially. The recommended level of magnesium in reef aquaria is 1180-1460. Magnesium is measured in mg/l (milligrams per litre) which is the same as ppm (parts per million).

Iodine (I): An important element for coral function, iodine is used by symbiotic algae that dwell inside both hard and soft corals. Although only necessary in trace amounts, a lack of iodine can have a significant effect on the pigmentation and health of corals, as well as being important to invertebrates such as shrimps and crabs. A good range of iodine to aim for in a marine aquarium is between 0.06 and 0.10. Iodine is measured in ppm (parts per million).

Please ask in our stores for more information regarding RO water or any other questions you may have related to testing your aquarium and pond water. Our teams will be happy to help!