Water quality is an extremely important concept in fish keeping, as deviations from ideal conditions can lead to direct or indirect damage to fish. By maintaining good water quality you can therefore keep your fish healthy & in top condition.
Water Quality Requirements Most fish keepers are aware of the need for maintaining certain water quality standards, in order to keep their fish healthy. Deviations from these requirements can lead to stress, physical damage, and eventually ill-health. For the purposes of keeping fish, it is perhaps useful to think of water quality in two parts — basic requirements and specific requirements.
To this might be added a basic pH range of 6.5-8.5, and a temperature range of around 24-27°C.
Basic requirements would be those that have to be maintained regardless of the species being kept, and which will ensure the health of most fish. For example, OATA’s guidelines are detailed in Table 1.
Table 1: OATA’s guidelines for basic water quality
Ammonia = <0.02mg/l NH3 (free ammonia)
Nitrite = 0.2mg/l
Nitrate = less than 50mg/l more than the level in your tap water
Dissolved Oxygen = 6mg/l
If these standards are maintained, the majority of freshwater tropical fish will remain healthy. These are the levels that ‘community’ aquaria should be maintained at.
However, it will be no surprise to more experienced fish keepers that some species will not do well even if these conditions are met. This is where more specific water quality requirements come into play. These are specific to the species of fish being kept, and are important for keeping wild-caught or especially sensitive fish, or for encouraging fish to spawn. Specific requirements would normally involve pH, general hardness (GH), carbonate hardness (KH), and perhaps nitrate and temperature. There are plenty of references for specific requirements, such as the series of Atlases by Baensch, which you can use to assess the needs of your fish. For example, the conditions in Lake Tanganyika suggest that cichlids from this habitat require a temperature of 24-29°C, pH of 8.6-9.5, GH of 11-17°dH, and a KH of 16-19°dH. In addition, it is often recommended that nitrate should be kept below 20mg/l.
When buying fish, you should ensure that you can meet their requirements for water quality. This will keep them healthy by avoiding stress and physiological problems.
Effects of Poor Water Quality
Deteriorations in the basic water quality requirements are the ones most likely to cause immediate problems for fish, with failure to meet specific requirements causing more subtle damage. There is not enough space to explore the issues surrounding each water quality parameter here, but two examples of specific problems include:
Gill Damage: Because of their delicate structure, and their close contact with the water, the gills are often one of the first structures to be damaged by poor water quality. For example, Kirk & Lewin (1993) found that the gill lamellae of rainbow trout began to deform, collapse, and clump together within 2hrs of exposure to ammonia (NH3) levels of 0,1 mg/l. Other pollutants, e.g. suspended solids, nitrite, heavy metals, chlorine, can also cause similar damage to the gills. An increase in mucus secretion around the gills, along with physical damage to their structure, makes it harder for fish to extract enough oxygen from the water. It also affects their ability to regulate the removal of excess fluid from the body, which is why extensive gill damage can result in dropsy.Internal Damage: Poor water quality may also cause internal damage. Chronic exposure to unsuitable ammonia levels will, for example, result in kidney damage and changes to the blood, such as a decrease in the number of oxygen- carrying red blood cells. Nitrite is well known for its effects on the oxygen- carrying capacity of the blood. It causes haemoglobin within the red blood cells to change into methaemoglobin, which is incapable of delivering oxygen to the internal organs.
Dealing with Water Quality Problems To keep our fish in good condition, it is necessary to maintain correct water quality at all times. This is one of the most important rules in fish keeping. However, from time to time even the most experienced aquarist will suffer some form of water quality problem. At such times it is knowing how to deal with the problem effectively that can mean the difference between healthy and unhealthy fish. Here are some tips on dealing with water quality problems:
Tip 1: Test your water regularly, especially at key times such as when setting up a new aquarium. For community aquaria, regular testing of the basic requirements will maintain health. For more sensitive species, more regular and comprehensive testing will be needed. This will ensure you identify problems early, before they have chance to cause irreversible damage.
Tip 2: Get extra aeration into the aquarium, and ensure the oxygen level remains above 6mg/l. This will help to overcome the reduced efficiency of the gills, and will also help to reduce the toxicity of any pollutants. This is because at high oxygen levels, the frequency with which water is passed over the gills is reduced, and thus contact with the toxin is reduced.
Tip 3: Have back-up equipment available, as the cause of the problem might be due to a broken filter or heater. Having a spare heater is especially important, as it is hard to keep the aquarium warm for long periods, whereas you can do something about ammonia and nitrite build-up. If the temperature is allowed to fall outside the ideal range, the immune system will slow down leaving the fish vulnerable to infection.
Tip 4: For high levels of ammonia and nitrite, water changes are a good short-term solution. Use water that has been conditioned and warmed to the same temperature as the aquarium. If you are keeping very sensitive fish, bear in mind that you will need to use water that is carefully adjusted to their requirements.
Tip 5: If you have salt-tolerant fish in the tank (check with your aquatics outlet), adding aquarium salt can mitigate the toxicity of ammonia and nitrite. 1g per litre of water would be plenty to start with. This is normally only recommended for goldfish though.
Tip 6: For some water quality parameters you can buy special resins that will reduce their concentration. Ammonia can be removed using certain zeolites, and heavy metals can be taken out with activated carbon. Using these as a temporary measure can help while the real cause of the problem is resolved.
Of course, once you have rectified the immediate problem, you must determine the underlying cause and resolve it. However, these tips will help you to cope in an emergency.