Last Updated: September 29, 2026
The size of a dosing pump is its dose envelope and duty cycle, not its physical body or a tank-gallon rating. Working out what size dosing pump do you need means sizing from your daily volume, event count, and flow needs, so this guide gives the ranges and simple formulas to match a pump to the actual dosing job.
As an Amazon Associate we earn from qualifying purchases.
By David Nguyen
Quick answer: Our top pick in 2026 is the 120 mL/day, 24 events — our #1 rated choice. See the full ranked comparison, alternatives and buying advice below.
Size the Dose Envelope, Not the Tank
A dosing pump is sized by the volumes and timing it must deliver, so start from your daily dose, how many events you split it into, and how fast each event must run. The lookup table below turns those inputs into results, and the sections after it show how to work each figure for your own routine and hardware.
| Input | Result | Note | Exception |
|---|---|---|---|
| 120 mL/day, 24 events | 5 mL per event | Must exceed pump minimum | Example only, not a rule |
| 5 mL at 15 mL/min | ~0.333 min ≈ 20 sec | Use calibrated flow | Nominal flow differs |
| Need <1 mL per event | 1 mL-minimum pump too coarse | Choose a finer minimum | AUTOAQUA 1 mL floor |
| Continuous feed or AWC | Continuous-duty pump | Not an intermittent doser | Versa runs continuous |
Start From Actual Daily Demand
The daily demand comes from testing and the product protocol, not from tank gallons, so establish it before sizing anything. Red Sea’s calculator bases the amount on measured calcium uptake, so two tanks of the same size can need different daily volumes, making your own test results the starting figure for sizing.
With the daily figure in hand, you can check it against each pump’s total range. A ReefDose head covers 0.2 to 1000 mL per day and an AUTOAQUA head 1 to 999 mL, so confirm your measured demand sits comfortably inside the range you are considering rather than near either extreme, where accuracy and headroom suffer.
Choose the Number of Heads
Head count follows how many liquids you dose independently, and it is part of sizing because each liquid needs its own envelope. A two-part routine needs two heads and a four-part regimen four, so a single wide-range head cannot substitute for multiple channels, and sizing must be done per liquid, not in total.
Size each head to the liquid it will dose, since amounts and minimum steps can differ between them. One liquid might need a fine sub-milliliter step while another doses several milliliters, so a pump whose per-head envelope suits every liquid you assign it is correctly sized, whereas averaging leaves one underserved.
Calculate Dose per Event
Splitting a daily dose into several events changes the size each event must deliver, so calculate it directly. The dose per event is the daily dose divided by the number of events, so 120 mL a day split across 24 events is 5 mL per event, a figure that must stay above the pump’s minimum to be deliverable.
Use the per-event figure, not the daily total, to check the pump’s minimum dose. More frequent splits make each event smaller, which can push it below a coarse pump’s floor, so a routine with many small events needs a finer minimum step, while fewer, larger events give more room within any pump’s envelope.
Check Minimum Dose and Runtime
Two checks finish the sizing: the event must clear the pump’s minimum, and its runtime must fit your schedule. Runtime per event is the dose volume divided by the calibrated flow rate, so 5 mL at 15 mL per minute takes about 0.333 minutes, roughly 20 seconds, using real calibrated flow rather than the nominal figure.
Confirm both that the event sits above the minimum and that its runtime fits between scheduled doses. If a liquid needs less than 1 mL per event, a pump with a 1 mL floor like the AUTOAQUA is outside the envelope, so choose a finer minimum, since the smallest event, not the daily total, decides suitability.
Adjust the Size for Your Situation
The base sizing gives a starting envelope, but real routines shift it, so adjust for how you split doses, the duty cycle, and the accuracy you need. These sections show how each factor tightens or loosens the envelope, so you can size up or down from the table rather than treating one figure as fixed for every tank.
Splitting Doses Changes the Event Size
How finely you split the daily dose directly changes the event size, and with it the minimum a pump must clear. More events mean smaller doses each, so a daily amount that is comfortable in four events may fall below a pump’s floor in twenty-four, which is why the split schedule is part of sizing, not an afterthought.
Decide your split first, then size the minimum to the resulting event, not the daily total. If you want frequent small doses for stability, favor a finer minimum step; if a few larger doses suit you, a coarser pump has room, so let the schedule you actually plan to run set the floor you need.
Intermittent Versus Continuous Duty
Duty cycle reshapes sizing because a continuous task is measured in sustained flow, not per-event volume. An intermittent additive routine is sized by dose envelope, while a reactor feed or water change is sized by continuous rate, so a Versa at up to 200 mL per minute is sized very differently from a scheduled doser.
Identify the duty before sizing, since the two use different figures entirely. For scheduled additives, size the dose envelope and minimum; for continuous jobs, size the sustained flow and confirm a steady-run rating, so matching duty to task avoids sizing an intermittent pump for a continuous role.
Accuracy Tightens the Envelope
Required accuracy narrows which pumps fit, because a tight tolerance matters most at small doses. A plus or minus 0.05 mL pump like the ReefDose holds a fine dose closely, while a plus or minus two percent unit drifts more on tiny amounts, so required accuracy effectively raises a coarse pump’s practical minimum.
Weigh the accuracy your liquids demand against the event size, since a small event with a loose tolerance can swing meaningfully. For fine additive dosing choose a tighter accuracy, and for larger, forgiving doses a looser figure is fine, so let the smallest event and its sensitivity decide how tight the pump must be.
When to Size Up or Down
Size up when your demand sits near the top of a pump’s range or your largest event needs more flow, and size down when a coarse minimum overshoots small doses. Leaving headroom at both ends keeps dosing accurate and gives room to grow, so avoid a pump that only just fits your current figures at either extreme.
Reassess sizing as the tank changes, since consumption rises with growth and stocking. A pump sized for a young tank may run near its limits later, so choose an envelope with margin, and remember the example numbers here are arithmetic illustrations, not a prescription that a given tank needs a specific daily dose.
Dosing Pump Sizing FAQs
These questions come up when keepers try to size a doser. Each answer leads with the direct call, then the condition that changes it, so you can size from your own daily volume, event size, and duty cycle rather than from tank gallons or a headline flow figure that does not reflect the real job.
How do I know what size dosing pump I need?
Size by the dose envelope and duty cycle, not the tank. Establish your measured daily demand, decide how many events you split it into, and calculate the dose per event, then confirm that event clears the pump’s minimum and its runtime fits your schedule, so the pump is sized to the job rather than the gallons.
Add duty cycle to finish the picture, since a continuous task is sized by sustained flow instead of per-event volume. For scheduled additives, size the envelope and minimum; for a continuous feed, size the rate and confirm continuous-duty rating, so the right size falls out of the volumes and timing you actually run.
Does tank volume tell me the pump size?
No. Tank gallons do not set the dose, so they do not size the pump. Consumption sets the daily amount, which Red Sea derives from actual uptake, so two same-size tanks can need different sizes. Measure your real demand and size from the dose envelope rather than reading a pump size off the tank volume.
Treat tank size as background only, never a formula. The sizing inputs are daily volume, event count, minimum dose, and duty cycle, all measured or chosen from your routine, so a large tank with light dosing can need a smaller envelope than a small tank with a heavy, frequent schedule.
How do I calculate dose per event and runtime?
Divide the daily dose by the number of events for dose per event, then divide that by the calibrated flow for runtime. So 120 mL a day over 24 events is 5 mL per event, and 5 mL at 15 mL per minute is about 0.333 minutes, roughly 20 seconds, using the units of millilitres over millilitres per minute.
Use calibrated real flow, not the nominal figure, and keep the units consistent so the result is in minutes. These numbers are arithmetic examples, not a rule that any tank needs 120 mL a day, so plug in your own measured demand and schedule to size the pump to your actual routine.
What if my dose is smaller than the pump minimum?
Then the pump is too coarse and outside your envelope, so choose one with a finer minimum. If a liquid needs less than 1 mL per event, a 1 mL-floor pump like the AUTOAQUA cannot place it, so a finer step, such as the ReefDose 0.2 mL, is required for that routine to work as intended.
Alternatively, split the daily dose into fewer, larger events so each clears the minimum, if your protocol allows it. Weigh whether frequency or a finer pump suits you better, since both solve a too-small event, but only within what your supplement schedule and stability goals actually permit for the tank.
Final Thoughts
The answer to what size dosing pump do you need is set by your dose envelope and duty cycle, not the tank: measure the daily demand, split it into events, check each event against the minimum and its runtime, and match the duty. Treat the example numbers here as illustrations, not a rule for any tank.
Ready to decide? Our #1 pick for 2026 is the 120 mL/day, 24 events.
Live price & availability on Amazon.
Related Reviews & Guides
Best Inline Heater for Sump Systems: Safe Smart Top Picks
How to Choose an Aquarium Sump: Top Expert Buying Guide
