The particular balance of chemicals in the aquarium. There are many factors that must be accounted for in determining how best to monitor the aquarium.

Factors involved in the aquarium include the following:

Water Quality in a Closed Aquarium

In a closed aquarium system, such as a reef tank, certain measures must be taken to ensure that the water in the tank is as close as possible to ideal conditions that may be found in nature. A very delicate balance must be found. There are many organic and inorganic compounds that must and mustn’t be found in a closed aquarium.


No ammonia should be present in an aquarium unless it is during the cycling period in which the bacteria responsible for breaking down wastes have yet to establish themselves. There must be a sufficient amount of bacteria in the tank to break down all the ammonia created by the organisms, or ammonia and other harmful wastes will accumulate. To allow these bacteria to grow, a long enough cycling time, and a source of food (ammonia) must be given to the bacteria.

Small amounts of ammonia can be added to the tank if the tank has no organisms in it, or one or two small fish may be placed in the tank to supply the food. Ammonia should not be present in an established tank. If it is, the bio-load is too high, or a proper cycling time was not allowed.

Ammonia/ammonium becomes more toxic at higher pH levels, and is therefore more dangerous to marine aquariums. The presence of ammonia is a cause for concern and can be remedied easily in three ways:

1. Decrease bio-load. Animals should be gradually added to tank. A period of time should be allowed between organisms so bacterial levels can adjust.

2. Increase biological filtration. This may include changing filter medium, adding a canister filter, and/or aerating filters.

3. Regular water changes!!

Medications such as antibiotics can kill beneficial bacteria, and should only be used in the case of an emergency.


Nitrates are the end product of organic breakdown of ammonia and detritus (waste products and dead organic material) that is formed in an aquarium. These can be detrimental to an aquarium. In large amounts, they may be toxic, and they are often associated with disease outbreaks in tanks because of the stress on the organisms and the poor water quality. Although freshwater tanks may be able to handle higher amounts of nitrates for short periods, corals and invertebrates are much more sensitive. Therefore, nitrates in a reef tank (freshwater also) should be kept as close to zero as possible.

Max. Acceptable Levels:
Nitrate (-NO3): 5 parts per million (PPM)
Nitrogen-nitrate (N-NO3): below 1 PPM (Most tests measure the N-NO3 levels)

Nitrates in a tank are not easily reduced to 0 PPM, but regular and frequent water changes should reduce the amount in the tank. Regular water changes should be used as a preventative measure to ensure nitrate levels do not get too high. Overfeeding and overcrowding can contribute to high nitrate products, as can detritus that accumulates in uncleaned gravel. A high tank temperature, 78F+, dead plants, or dead animals can also produce higher nitrate levels.


The information for nitrates also applies to organic chemicals called phosphates. The maximum level of phosphate (PO4) in a tank is about 0.1 PPM. High levels of PO4 may stress fish and cause blooms of unwanted algae, therefore, the phosphates should be kept as close to zero as possible. Care must be taken that salt, water, or other additives to the tank do not contain phosphates.


Nitrite levels should always be at 0 PPM unless a tank is cycling. Nitrite interferes with oxygen metabolism and is toxic to fish and other invertebrates. Nitrite levels higher than 0.01-0.1 PPM indicate that the biological filtration (i.e., the good bacteria) in the tank is insufficient to handle the amount of wastes produced by the organisms in the tank. Dirty mechanical filters can contribute to this problem

Nitrite normally appears when new organisms are added to a tank because of the increase in the bio-load. The nitrites should not be present for longer than a week, and they should only occur in small amounts. If the nitrite level stays high after an organism is added, it indicates that the tank is overcrowded.

Nitrite is frequently overlooked as a cause of low water quality and problems in tanks, but tests should be done about once a month or so to make sure that the levels are not too high.

Dissolved Oxygen

Oxygen is necessary to all life in marine and freshwater aquariums. Important biological processes in the filter require oxygen. Invertebrates and fish both need large amounts of oxygen in order to survive. The dissolved oxygen (D.O.) levels in a tank should be kept at 6 - 10 mg/LTo prevent the loss of dissolved oxygen in a tank, certain precautions can be taken:
1. Clean filters at least once a week to prevent decay that can take up oxygen.
2. The tank temperature should be kept on the lower side (less than 77F) so that the metabolisms and waste products of the organisms aren’t too high.
3. Do not overfeed; excess food will decay.
4. Do not overcrowd.
5. Remove dead organisms and dead algae.
6. Use some system of aeration (air stone, trickle filter, etc.)
7. Maintain good water circulation in tank.


Chlorine is added to tap water by treatment plants to prevent harmful bacteria from growing and causing disease. This chlorine however is toxic to fish and must be removed from the water before using the water in an aquarium.

Chlorine naturally dissipates into the air, so an easy method of removing chlorine is by aerating the water for a day before using it for water changes, etc. Some products containing sulfur compounds are also effective at quickly removing chlorine, are safe to use, and completely non-toxic. These products, however, may cause slight changes in pH levels.

Log in or registerto write something here or to contact authors.