Each aquatic animal species has a preferred water temperature range. This preferred temperature range may vary at different stages of the life cycle. Animals need to be kept in their preferred temperature range for optimum growth. Animals kept in temperatures lower than their preferred range often stop feeding.

Organic processes are dependant upon temperature - eg increase the water temperature by 4 degrees Celcius and the bacteria activity can double.

Water Hardness

Rain water is considered to be soft as it lathers easily with soap and has low levels of Calcium and Magnesium salts.

Water hardness is measured in different units which vary from country to country. (See conversion table below ) Generally only the statutory units ( SI units ) are used in business and commerce. The SI units are measured in mol/l.

Alkaline Alkaline German ppm of British French earth earth degree of of degree degree ions ions hardness CaCO3 mmole/l meq/l d

• 1 mmole/l of alkaline earth 1.00 2.00 5.6 100.00 7.02 10.00 ions
• 1 meq/l of alkaline earth 0.50 1.00 2.80 50.00 3.51 5.00 ions
• 1 German degree of hardness d 0.18 0.357 1.00 17.80 1.25 1.78
• 1 ppm of CaO3 0.01 0.020 1.056 1.00 0.0702 0.10
• 1 British degree 0.14 0.285 0.798 14.30 1.0 1.43
• 1 French degree 0.10 0.200 0.560 10.00 0.702 1.0
• Total hardness ( degrees of d ) Evaluation
  0 - 4 very soft
  4 - 8 soft
  8 - 18 medium hard
  18 - 30 hard
  30 + very hard
• meq/l Milligram-equivalents per litre
• mmole/l Millimols per litre

When using the German hardness units ( d ) note that no CaO is present in aqueous solution but that all hardness formers are calculated as CaO

(Source Merk )

Buffering

Water that has high levels of Calcium Carbonate ( CaCO3 ) is considered to be well buffered as it resists changes in pH ( the level of acidity or alkalinity )