Calculate recirculating rack system turnover rate, per-tank flow, and daily water exchange volume. Includes pump derate factor and commissioning checklist for aquatic facilities.
Try it out
Load example Rack Turnover Planner data to see the full workflow
Recommended: 4-6 turnovers/hr for zebrafish
When to use
Do not use for
Pump nameplate flow is measured at zero head (no vertical lift, no pipe friction). Real installations lose 15-25% of rated flow. A 10 LPM pump may deliver only 7.5-8.5 LPM at typical rack head heights. Measure actual flow during commissioning.
The sump is part of the total system volume. A larger sump dilutes waste between filtration passes but also increases the volume the pump must turn over. Size the sump for at least the total drain-down volume of all tanks.
A system may achieve adequate total turnovers while individual tanks — especially those far from the pump — receive very little flow. Measure flow at inlet, middle, and far-end tank positions during commissioning.
Turnover recirculates the same water through filtration. Water exchange replaces a portion of system water with fresh pre-treated water. Both are necessary: turnover for continuous filtration, exchange for diluting what the biofilter cannot remove.
Effective pump flow = rated flow x (1 - derate%). Total system volume = (tank volume x count) + sump. Turnovers/hr = (effective flow x 60) / system volume. Daily exchange = system volume x exchange%. Warnings triggered at <target turnovers, >10 turnovers/hr, or <50 mL/min per tank.
Published 2026-04-06. Calculations support planning and documentation; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience Aquatic Rack Turnover & Water Exchange Planner. ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/aquatic-rack-turnover-calculator
Lawrence C. The husbandry of zebrafish (Danio rerio): A review. Aquaculture. 2007;269(1-4):1-20.
Harper C, Lawrence C. The Laboratory Zebrafish. CRC Press. 2011.
Recirculating aquatic systems (RAS) continuously pump water from tanks through a treatment loop — typically including mechanical filtration, biological filtration (nitrification), UV sterilization, temperature control, and gas exchange — before returning it to the tanks.
Under-sizing the pump is the most common design error. Always calculate based on derated flow, not nameplate capacity.
Daily water exchange (also called make-up water or fresh water replacement) dilutes accumulated waste products that the biofilter cannot fully remove — primarily nitrate, dissolved organics, and hormones.
Make-up water must be pre-treated to match the system's temperature, pH, and conductivity before introduction. Rapid large-volume changes can shock fish and destabilize the biofilter.
