Common Terms

DO (dissolved oxygen)

Measured either as an absolute value in milligrams of Oxygen per litre of water (mg/l) or as a relative value - the percentage of Oxygen dissolved in the water compared to the maximum amount of Oxygen that could be dissolved in the water at that temperature and pressure.

Typical values in a reasonable recirculating system would be 8 mg/l or 85 - 95% at 24 degrees Celcius

pH (the measure used for how acid or alkaline the water is) If you are feeding heavily expect the pH to keep dropping and you will need to add bicarbonate of soda to maintain the pH at the target level.

Temperature - usually measured in degrees Celcius.

Temperature is one of the critical water quality parameters and is often not given enough attention. Fish generally require a very narrow range of temperatures for optimum feeding and growth particularly in their early development stages.

EC ( Electro Conductivity ) measured in milliSiemens per Centimeter squared ( mS/cm2 ) or in microSiemens per Centimeter squared

as a rough guide 1 EC unit ( 1 mS/cm2) is equivalent to 640 PPM ( parts per million ) of dissolved salts

Salinity - expressed as either PPT ( parts per thousand ) or as a percentage salinity

Seawater is about 35,000 PPM ( 35 PPT ) or 3.5%

TAN - total ammonia nitrogen ( includes ionised and un-ionised ammonium ) the un-ionised part is very toxic to most aquatic animals and the percentage of un-ionised ammonium increases as temperature and pH increase.

NO2 - nitrite - toxic to aquatic animals at very low levels - parts per million

NO3 - nitrate - not so toxic but levels generally need to be below 150 PPM (parts per million)