Measurements

mg/l and PPM are roughly equivalent

HRT - hydraulic retention time - how quickly the water is recirculated in a system - generally every 60 minutes

SSA - specific surface area - the measurement of bio-filtration material - the surface area in metres squared of a cubic meter of the material - generally values greater than 260 m2/m3 are usefull

DNR - design nitrification rate - measured in gms/m2 - the number of grams of TAN consumed by a bio-filter per day - generally measured as grams of TAN consumed by m2 (square metres of surface area) of biofilter medium per day.

FCR - Food Conversion Rate - the rate at which food fed to the fish is converted to increased fish biomass - a rate of 1.5 : 1 means 1.5 kgs of food is converted by the fish to 1 kg of increased weight.