The primary requirement for maintaining aquatic organisms is water quality. The water supply must be free of pollutants, including sewage and industrial wastes, and it should be in gaseous equilibrium with the atmosphere to ensure adequate oxygen and to avoid supersaturation with nitrogen. In recirculating systems, water treatment must not only ensure clarity of the water but also purification of metabolic wastes (fish poo!)
Water is continuously recirculated in most systems and is only renewed periodically. Metabolic wastes must be treated since they are not continuously flushed from the system. An important problem is that ammonia must be rapidly removed or transformed because it is harmful even at very low concentrations. In the aquarium the bacteria that convert ammonia to nitrite reside primarily in the filter material, and an under gravel filter with a large surface area is usually provided to ensure their abundance. Plant growth in the aquarium is not usually sufficient to utilise all the nitrate produced by bacteria from nitrite. Although some aquariums have operated many years with a minimum of water renewal, it is normally necessary to replace 25-30% of the aquarium water every four weeks to maintain a low level of nitrates. The use of charcoal in both fresh water and seawater systems helps to slow the accumulation of nitrogenous wastes.
Any water you add to your aquarium should be clean and chlorine free. The water we get from our taps in the UK has been treated with chlorine, good news for us, but not for the fish! If you allow the water to stand for at least 24 hours the chlorine should disperse, this can be speeded up slightly by aerating the water with an air pump and air stone. Chlorine isn't the only chemical added to our drinking water, chloramine is another. Unfortunately this is more difficult to remove as it does not disperse naturally. You will need to add an aquarium conditioner such as Stress Coat™. The conditioner will remove both the chlorine, chloramine and neutralise any heavy metals present in the tap water.
It is worth asking about the water in your local area. Here in Fleetwood we are lucky to have a neutral pH so for fish keepers who have community tanks, it's a simple matter of de-chlorinating. The pH scale is used to discover the acidity/alkalinity of the water. The pH scale runs from 0 (acidic) to 14 (alkaline) with 7 being described as neutral. The pH scale is a 'logarithmic' scale. This means that each step on the scale is 10 times the previous step. So a pH of 6 is actually 10 times more acidic than a pH of 7. Test kits can be bought to monitor water conditions, it is very important to test on a regular basis as water chemistry will alter over time. Most aquatic retailers will offer a testing service, take a sample of water from the aquarium in a clean container into the shop and for a small fee they will test it for you. If you choose fish that require different water parameters to your water supply you will have to alter the chemistry accordingly. There are a wide range of products available to help you do this easily.
The easiest way to fill your aquarium is with a jug. Place a saucer or flat stone on top of the substrate and slowly pour water onto it. The saucer/stone helps to prevent disturbing the gravel. This can be time consuming but it saves destroying your layout. Once the aquarium is approximately one third full you can start to slowly pour the water in from a bucket, ensuring that the gravel is not disturbed.
Like all living things fish and plants need oxygen to live. Oxygen is obviously scarce in the aquatic environment. It is important to circulate your aquarium well, so that it takes oxygen up from the surface and gets rid of poisonous waste carbon dioxide. Whilst filters effectively circulate aquarium water, the best way to ensure optimum gaseous exchange in your aquarium is to use an air pump and air stones. An additional benefit to using an air pump is the attractive aesthetic effect of air bubbles and the option to run air powered ornaments.