Fish Care - Monitoring Water Quality

by Rupert Bridges, Tetra Information Centre

There's an old saying that fishkeeping is not about keeping fish, but keeping water. In many ways this is true, as unless we keep their water in good condition, our fish will not remain healthy and happy.

Having an understanding of water quality will help you to be a better fishkeeper. It can help you avoid problems, and resolve them quickly if they do occur. After all, most fish health problems are caused through poor water quality. This article will introduce you to the most important water quality parameters, show you how to measure them, and suggest what to do if they are not correct.

The nitrogen cycle
The nitrogen cycle is central to the health of the aquarium, and involves three of the most important water quality parameters: ammonia (NH 3 / 4 + ), nitrite (NO 2 - ), and nitrate (NO 3 - ). In creating a healthy aquarium, we are trying to get part of the nitrogen cycle to work inside our filter. The following diagram illustrates the key stages in the nitrogen cycle for aquariums:

Both ammonia and nitrite are toxic to fish, and will cause health problems. By getting specific parts of the nitrogen cycle to work within the filter, ammonia and nitrite are converted into nitrate, which is virtually harmless to most fish. This is called ‘biological filtration'.

High ammonia and nitrite levels are common in new aquariums, or when the aquarium is overstocked or overfed. If left unchecked, levels may rise, resulting in the outbreak of disease and / or the loss of fish. It is therefore important to regularly test the water for ammonia and nitrite, as otherwise you cannot tell what the levels are (clear water can still be polluted). This is especially important for new aquariums.

Both ammonia and nitrite can be tested for using TetraTest water quality kits. They are simple to use, and offer a quick way of finding out how healthy the water is. Ideally, levels of both ammonia and nitrite should be 0mg/l. If ammonia levels rise above 0.25mg/l, or nitrite rises above 0.3mg/l, a partial water change should be performed to dilute them. Remember to always use water that has been conditioned with a dechlorinator, such as AquaSafe. Having reduced levels, you should then seek advice as to the cause of the water quality problem.

For new aquariums, ammonia and nitrite should be checked every day or two. In ‘mature' aquariums, testing can be reduced to once every 1-2 weeks. A healthy aquarium should have no ammonia or nitrite.

Nitrate is the end product of the biological filtration that occurs in the filter. It is relatively harmless to fish, and is a key nutrient for plants. However, if left unchecked, it can begin to stress fish, and will encourage the growth of algae. For most fish, a nitrate level of 50mg/l or below is ideal. Sensitive species such as discus prefer lower levels. You can test for nitrate using TetraTest kits, and if levels are too high you can take steps to reduce them. These might include cleaning the gravel, ensuring you are feeding a low-waste food such as TetraMin Pro, adding more plants, performing a water change, or perhaps using a nitrate reducer, such as Tetra NitrateMinus. As a general rule, nitrate levels should be tested every 2-3 weeks.

pH
pH is an measure of how acidic the aquarium water is. It is expressed on a scale of 0 to 14, with 7 being neutral – i.e. neither acidic or alkaline. The numbers refer to the concentration of hydrogen ions in the water. Water is made up of hydrogen ions (H + ) and hydroxyl ions (OH - ), hence the formula for water being H 2 O. Water naturally dissociates into H + and OH - ions. If more H + are present, the water becomes acidic (pH 0 - <7), if there are more OH - , the water is alkaline (pH>7 – 14). If they are present in equal numbers, the pH is 7 (neutral). The pH scale is called a logarithmic one, meaning that for every increase or decrease of one unit, there is a ten-fold change in the concentration of hydrogen ions. Therefore, even seemingly small changes in pH can have large effects.

Different species of fish have evolved in different habitats, which differ in their pH levels. For example, the Blackwaters of the Amazon have pH levels around 6.0 or lower, whilst Lake Tanganyika in Africa has a pH of 8.5-9.0. Most fish species come from waters with a pH level somewhere in the range of 6.5-8.5.

If you intend to keep sensitive or wild-caught species, or you want to breed your fish, you will need to provide them with a natural pH. However, the vast majority of aquarium species are farm-raised, and far less sensitive to pH than their wild counterparts. For these fish, the golden rule is to keep the pH stable, within the range of 6.5-8.5. In most cases, it is fluctuations in pH that cause far more damage than the pH level itself.

The stability of the pH level is affected by a range of factors, such as the ‘buffering' capacity of the water (its ability to resist changes in pH), stocking levels, plant growth, feeding rates, and so on. The only way of telling if the pH is stable, is by testing the water. Failure to identify a fluctuating pH can lead to fish stress, and eventually ill health.

Fortunately, it is very simple to check pH levels, using a TetraTest pH kit. When you first set up an aquarium, you should check the pH to ensure it is within the safe range for the fish you want. Once the aquarium becomes more heavily stocked, it is more likely that the pH may start to fluctuate. In a mature aquarium, the pH should be checked every 1-2 weeks. It is important to test the pH level first thing in the morning, before turning the lights on, as well as towards the end of the day, before turning them off. This is because the process of photosynthesis (performed by plants and algae during the day) can affect pH.

If the pH level is fluctuating by more than 0.5 units during the testing period, you need to seek advice on how to stabilise it. This may involve checking plant and algae growth, or increasing the buffering capacity of the water.

Other water quality parameters
In addition to those mentioned, there are also other water quality parameters of importance to fish. There is no space to mention them all here, but they include oxygen and mineral content. Oxygen is essential to the health of the aquarium, and you should ensure that plenty of aeration is provided. However, it can still be a good idea to test levels from time to time. The mineral content of the water is closely linked to pH levels, and is especially important for sensitive fish such as discus. As you get more experienced, it is well worth expanding your testing equipment to include these parameters.

To start with though, concentrate on the four key parameters: ammonia, nitrite, nitrate, and pH. By checking these regularly, you will be a much better fishkeeper, and your fish will in turn reward you with greater health, condition, and colouration.