Calculate recirculating rack system turnover rate, per-tank flow, and daily water exchange volume. Includes pump derate factor and commissioning checklist for aquatic facilities.
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Recommended: 4-6 turnovers/hr for zebrafish
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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.
Last validated 2026-04-06. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience Aquatic Rack Turnover & Water Exchange Planner (v1.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/aquatic-rack-turnover-planner
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.
Recirculating rack systems with integrated filtration and UV sterilization
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