Recirculating System Design

Recommended Tank Volume depends on exactly one input — Fish Biomass — using a 0.5 lbs-fish-per-gallon rule of thumb common for intensive RAS stocking density. Feed Rate and Target Water Temperature have zero effect on it. Biofilter Media Area instead depends on Fish Biomass and Feed Rate together: it works backward from daily feed (biomass times feed rate as a percentage of body weight) through an assumed 3% total-ammonia-nitrogen (TAN) production rate and a fixed nitrification rate per square foot of moving-bed media, so both a bigger fish load and a higher feed percentage push it up, and Target Water Temperature never enters that calculation at all — this calculator does not model how nitrification efficiency actually varies with temperature, which real biofilters do.

Pump Flow Rate and Total System Volume follow from tank size plus biofilter size plus an assumed 20% sump allowance, turned over at a fixed 1.5 times per hour — again with no temperature dependence. Heating/Cooling Load is the one output that does use Target Water Temperature, comparing it against an assumed 20°C (68°F) room temperature and scaling the load by the size of the difference in either direction — set the target near 68°F and the estimated load shrinks toward zero; move it further away in either direction (colder or warmer) and the load grows. None of these are substitutes for site-specific engineering: real biofilter sizing accounts for pH, alkalinity, and species-specific ammonia tolerance that this simplified model omits.