Ammonia (NH3) - is primarily the dissolved waste products of fish. Ammonia is highly toxic to fish and causes damage to the gills, very high concentrations can cause brain damage and death.

Nitrite (NO2) - is produced by bacteria called nitrosomonas. The nitrosomonas use the oxygen from the water to convert ammonia (NH3) and ammonium (NH4 ) into nitrite which is still highly toxic to fish. It consists of 1 atom of nitrogen and 2 atoms of oxygen.

Nitrate (NO3) - is produced by bacteria called nitrobacter. The nitrobacter again use the oxygen from the water to convert nitrite (NO2) into nitrate which is far less toxic to the fish. It consists of 1 atom of nitrogen and 3 atoms of oxygen.

When an aquarium is first set up the first to peak is the ammonia levels. As the filters start to mature the nitrosomonas begin to multiply and deal with the ammonia. This then causes a second peak of nitrite. The nitrobacter then begins to multiply which in turn deals with the nitrite converting it into the more harmless nitrate which must be controlled by the aquarist by regular partial water changes.

pH - The measurement of how acid or alkaline the water is. The most acid solution being denoted 0.0 and the strongest alkaline solution being 14.0. Pure distilled water being neither acid or alkaline has a value of 7.0

This value is important to a number of delicate species of fish all the time and to many others when breeding. Sudden drastic changes in the pH value can kill fish, so care should be taken when introducing new fish to a tank. Testing kits are reasonably accurate and easy to use and there are a number of chemicals available to alter the pH value.

Hardness - Often confused with pH since soft water tends to be acidic whilst hard water tends to be alkaline, however, the two values are actually independent.

Hardness is measured on a scale where 1 degree of hardness=14.3 parts per million of Calcium carbonate. Another way to express hardness is in parts per million of Calcium carbonate. Up to 6 dH or 100ppm is considered soft whilst over 25 dH or 450ppm is very hard. Again there are good test kits on the market and a number of methods to raise or lower the hardness.

Chlorine - This and other additives in tapwater can create a problem if at high levels in your supply. Watch your local paper for announcements of when extra chemicals will be added to your supply and never do a water change if the tapwater is cloudy or there is an unusually high smell of chlorine. Many preparations are available to render chlorine harmless to fish.

Chloramine.- This is a combination of chlorine and ammonia. Some water companies are using this instead of chlorine to disinfect the water supply. Chloramines are toxic to fish as is chlorine and must be removed. You may not have had to remove chlorine from your aquarium water because it disappears rapidly on its own. This is NOT the case with chloramines and steps must be made to remove them.

Most aquatic shops have sold dechlorinating agents for years and generally recommend using them. The chemicals used to remove chlorine should work just as well for chloramines. Chloramine levels in water used to keep fish should be kept below 0.1 mg/l. This can be measured with a total-chlorine test kit. If you are in any doubt whether your water company use chloramines, ring them and ask.

Dissolved Oxygen - Fish need dissolved oxygen in the water to breathe. This comes from aquatic plants and the water surface. Plants stop producing oxygen at night so they must be ignored when calculating numbers of fish for your aquarium. Aeration can significantly increase the number of fish a tank will support. However, if there is a power cut or the pump fails then the carbon dioxide level will build up as the oxygen level falls and a crisis point is quickly reached at which time the fish start to gasp at the surface and eventually die.

Chemical filtration - This is usually limited to the use of activated carbon which adsorbs waste products onto its surface. It must be replaced on a regular basis to remain effective otherwise the chemicals will start to leak back into the water. Adsorb means to hold particles of another substance to its surface where as absorb means to soak up or consume.

Mechanical filtration - This is to physically strain or remove particulate matter form the water. Methods range from simple plastic boxes using an airlift to pull water through a filter floss or sponge to power filters which pump the water through a sponge. All rely on regular cleaning of the filter medium.

Biological filtration- This is the process where bacteria break down wastes to less harmful nitrates. See Ammonia, Nitrite and Nitrate above.

Ion Exchange Resin - Imagine water resistant beads that act like magnets. Like any magnet, they are made up of particles that attract other particles according to their magnetic charge. The magnetic particles are called ions and the negatively charged ions in the beads are surrounded by positively charged ions of hydrogen.

The negative ions attract positive ions from the water, like a magnet. The ions being pulled are those you don't want like lead, copper, calcium, magnesium and nitrate which are exchanged for hydrogen or in some cases sodium.

Activated Carbon -Activated carbon is made by soaking organic material (usually coconut shells) in special solutions and super heating it without oxygen to produce a greater surface with lots of pores ... example: 1oz. of granular activated carbon equals 186,500 square feet of surface area (approximately 4 acres) ... this is why it is the ideal filtering substance best suited to take up the maximum of organic molecules. Activated carbon is used extensively in the food and medical applications and will remove chlorine, pesticides and other organic matter.

The carbon MUST be changed at regular intervals to remain effective.

Genus -Scientific name for a group or family of closely related life forms. It can be thougt of as a surname with the species as the foreneme. It is the first part of any scientific name and begins with a capital letter.

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