How to Calibrate a Dosing Pump
Finn Sterling, Reef Systems Editor
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Updated Aug 7, 2026
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5 min read
A dosing pump's rated output and its actual output drift apart faster than most people expect. Tubing stretches, roller heads wear, and a pump that's supposed to deliver 30 mL/minute can quietly slide to 25 or 35 within a few months. Calibration is how you catch that before it shows up as "unexplained" alkalinity swings.
What you need
A graduated cylinder (10-25 mL range is plenty precise), RO/DI water, and a stopwatch or your phone's timer.
Step 1: Prime the line
Run RO/DI water through the dosing tubing until every air bubble is out of the line, usually about 2 hours for a fresh setup. Air pockets compress under pump pressure instead of pushing fluid, which throws off every measurement after this point.
Step 2: Time a measured volume
Place the dosing line into the graduated cylinder and run the pump for a fixed time, long enough to move a measurable amount. A common approach: time how long it takes to move 10 mL. If that takes 20 seconds, you're looking at 0.5 mL/second, or about 30 mL/minute.
Step 3: Compare against what your controller assumes
Your dosing schedule is programmed around an assumed rate, either the manufacturer's spec or whatever you entered when you first set it up. If your measured rate doesn't match that assumption, every scheduled dose is off by the same percentage. A pump that's actually 15% slower than its display value delivers a slow, compounding under-dose that reads as "unstable alkalinity" for weeks before anyone traces it back to the pump.
Step 4: Adjust and re-test
Update your dosing schedule or controller settings to match the measured rate, not the rated one. Run the calibration test again to confirm the new numbers hold. Some controllers let you enter a calibration factor directly instead of recalculating your whole schedule by hand, which is worth using if yours has it.
After calibrating: re-run the Alkalinity & Calcium Dosing Calculator with your current readings. A freshly-calibrated pump combined with a stale dosing amount still won't hold your target steady.
How often to recalibrate
Once at setup, then monthly after that. Silicone and vinyl dosing tubing stretches and hardens with use, which changes how much fluid the roller head displaces per revolution even though nothing about your programming changed. A pump nobody's touched in six months is a pump nobody's actually verified in six months, and that's exactly the gap that shows up as "my alkalinity keeps swinging for no reason."