The word ecosystem defines the interactions that take place between the biological and non-biological elements within a defined space. The biological component of the ecosystem is called the biocenosis and represents all its living organisms; the non-biological part represents all its abiotic components (i.e. gas, minerals, elements in general) and is called the biotope.

Interactions, both internally and externally, occur and develop between the biocenosis and the biotope, and it is these interactions which define the ecosystem.

An aquarium can therefore be described as a closed artificial ecosystem in which fish and plants are able to find a habitat where they can grow and develop in a healthy and balanced way. Each aquarium must therefore be consciously designed, developed and managed to facilitate the establishment of the virtuous cycles that occur spontaneously in nature and give rise to the interactions.

Water: the importance of analysis

The main parameters that need to be considered and monitored, with regard to a freshwater aquarium, are:

• pH
• hardness
• ammonia
• nitrites
• nitrates
• phosphates

pH is the measure of the water's acidity. It is measured on a scale ranging from 1 to 14. Low values (up to 7) correspond to acidic waters.

A pH value equal to 7 indicates neutrality, that is, a balance between the acidic components and the basic component (for the latter, the index varies from 7 to 14).

For freshwater aquariums, the ideal pH varies greatly depending on the type of plants and fish it supports, but ranges approximately from 5.5 to over 8.0. Most tropical fish prefer medium or slightly acidic values. However, even when faced with a (non-sudden) change in this value, fish are able to adapt without difficulty, so much so that, in nature, the same species can be found in aquatic ecosystems with very different values.

A pH check is recommended at every partial water change.

Carbonate hardness is measured in KH; its function in the aquarium is to stabilise the pH of the water by opposing any sudden variations in it. A KH value between 4 and 8 is generally suitable for most freshwater aquariums; values below 4 expose the tank to the risk of sudden changes in pH. For marine aquariums, KH values range from 8 to 10. The KH value also affects the amount of CO₂ dissolved in the water and its assimilation by the plants. By knowing the KH and pH values of your aquarium, you can work out the amount of dissolved CO₂, thanks to the relationships that regulate these three amounts (see the table below).

Ammonia is one of the products of protein metabolism of fish: the proteins ingested with food are hydrolysed in the gut and broken down into amino acids. The amino acids are then transported by the blood to the cells, where they are used for protein synthesis. Those not used directly are broken down to produce energy; during this process, ammonia if formed, which, being highly toxic, is excreted directly into the water. It is found in two forms: ammonium, with a relatively low level of toxicity, and ammonia, which is extremely toxic. The concentration of ammonia/ammonium in the aquarium, with the exclusion of the set-up period, should ideally be zero. The presence of ammonia/ammonium – even at low concentrations – indicates poor biological filtration.

We recommend performing the Askoll NH₃/NH₄ Test once a week.