A dosing pump for a reef tank is an automated device that delivers precise, measured amounts of liquid supplements, typically calcium and alkalinity solutions, into your aquarium at set intervals throughout the day. If your corals are consuming more calcium and alkalinity than your water changes can replenish, a dosing pump is the most reliable way to keep those parameters stable without daily manual additions. This guide covers how dosing pumps work, when you actually need one, which type fits your setup, and how to dial in an accurate dosing schedule.
Running a reef tank with growing corals means watching your calcium and alkalinity levels creep down between water changes. In a lightly stocked tank with soft corals, bi-weekly water changes can keep up. But once you have a mixed reef with LPS and SPS corals, or an SPS-heavy tank, consumption outpaces what water changes supply. That's the point where manual dosing becomes tedious and inconsistent, and where a dosing pump earns its place.
What a Reef Dosing Pump Actually Does
The most common reef dosing application is two-part dosing. Two-part systems use two solutions: Part A (calcium chloride) and Part B (alkalinity, typically sodium bicarbonate or sodium carbonate blend). These are dosed in equal volumes to raise and maintain both parameters simultaneously. When dosed in balance, they don't affect pH or other water chemistry significantly.
A dosing pump automates this by delivering a set volume of liquid at a set time, typically spreading doses throughout the day in small increments rather than one large daily dose. Smaller, more frequent doses cause less parameter fluctuation than a single large dose.
Beyond two-part dosing, reef dosers are used to deliver:
- Amino acids and coral foods
- Bacteria supplements for nitrate and phosphate reduction (like Prodibio or NoPox)
- Iodine, potassium, and trace elements
- Top-off water (though dedicated ATO units are more precise for this purpose)
Types of Dosing Pumps
Peristaltic Pumps
Peristaltic pumps work by squeezing a flexible tube in a rotating motion, pushing liquid forward in precise measured volumes. They're the most accurate type for reef dosing because the volume per revolution is consistent, and they're easy to calibrate by running them into a measuring cup.
The BRS Dosing Pump, Kamoer X4S, Jebao DP-4, and Reef Octopus DOS are all peristaltic units popular in the reef community. The Jebao DP-4 is a solid budget option at around $70-$90 for a four-head unit. The Kamoer X4S offers WiFi control and smartphone monitoring for closer to $150-$200.
Gear Pumps
Gear pumps use interlocking rotating gears to move liquid. They're less common in the hobby because they're more sensitive to contamination and harder to clean than peristaltic pumps. When a gear pump starts dosing incorrectly, the cause is usually buildup on the gears, which requires disassembly to fix.
Gravity Dosers
Gravity dosers use timers to open valves on elevated reservoirs, letting liquid drip into the sump by gravity. They're the cheapest option but the least precise, since flow rate varies with reservoir level. For low-budget setups where rough dosing is acceptable, they work, but for SPS tanks where alkalinity stability within 0.5 dKH matters, a peristaltic pump is necessary.
When Do You Need a Reef Dosing Pump?
You need a dosing pump when your corals' daily calcium and alkalinity consumption exceeds what weekly or bi-weekly water changes can replenish, or when manual dosing is causing parameter swings that stress your corals.
A practical test: measure your alkalinity at the same time on two consecutive days without dosing or doing a water change. If it drops more than 0.5 dKH per day, manual daily dosing becomes error-prone and you'll benefit from automation. If it's dropping 1 dKH or more per day, a dosing pump is practically necessary for a stable SPS system.
As a rough reference point, SPS tanks at moderate stocking levels typically consume:
- Calcium: 20-50 ppm per week in a 75-gallon tank
- Alkalinity: 1-3 dKH per day in a 75-gallon tank with moderate-to-heavy SPS coverage
Two-part dosing at this consumption rate requires 50-200 mL per day of each part, which is straightforward to automate but tedious and inconsistent when done by hand.
Our guide to the best dosing pump for reef tank compares the top peristaltic units across accuracy, reliability, and price. If you're also evaluating multi-head options that handle more than two supplements, the best aquarium dosing pump roundup covers two-head through eight-head configurations.
How to Set Up a Reef Dosing Schedule
Step 1: Calculate Daily Consumption
Test your calcium and alkalinity every day for three to five days with your current coral load, without doing water changes or manual dosing. Track the daily drop. This gives you your actual consumption rate.
Step 2: Calculate Required Dose Volume
Two-part solutions typically raise alkalinity by 0.1-0.2 dKH per 1 mL per 10 gallons, and raise calcium by 2-4 ppm per 1 mL per 10 gallons, depending on the specific product. Check your product's instructions for its specific concentration. Divide your daily consumption by the dose rate to get your daily volume needed.
Step 3: Calibrate Your Pump
Run your dosing pump into a measuring cup for exactly 60 seconds at your intended speed. The volume delivered tells you the pump's actual mL per minute output, which may differ slightly from the rated spec. Use your measured output to set the dose time accurately.
Step 4: Spread Doses Throughout the Day
Rather than one large dose, split your daily volume into 4-12 smaller doses spread across the day. A pump dosing 60 mL of alkalinity per day, for example, works better as 6 doses of 10 mL every 4 hours than one 60 mL dose at midnight. This approach reduces the local pH and chemistry spike at the injection point and gives the whole tank water time to mix between doses.
Step 5: Verify and Adjust
After running your dosing schedule for 3-5 days, test your parameters again at the same time of day. If calcium or alkalinity is trending up or down from your target, adjust your dose volume accordingly in 10-15% increments. A stable reef runs within 10 ppm of target calcium and within 0.5 dKH of target alkalinity.
Dosing Pump Placement and Maintenance
Where to Inject the Dose
Always dose into a high-flow area of your sump rather than directly into the display tank. This mixes the solutions with a large water volume before they reach corals. Dosing two-part solutions directly onto corals causes a local chemistry spike that stresses or bleaches coral tissue immediately around the injection point.
Keep Part A and Part B inlets separated from each other. If they contact each other at concentration, they react and precipitate as calcium carbonate, which clogs your dosing tubing and pump heads.
Tubing Maintenance
Peristaltic pump tubing wears out over time as the rotating rollers compress it repeatedly. Most manufacturers recommend replacing the tubing every 12-18 months, or sooner if you notice changes in your parameters that suggest inconsistent dosing. Replacement tubing for most brands costs $5-$15.
Cleaning Pump Heads
Flush your pump heads with RO water monthly. Two-part solutions are concentrated and will crystallize inside the pump heads if left to dry out. Crystallization inside the head causes irregular dosing and eventually damages the tubing.
FAQ
Do I need a dosing pump if I do large water changes? Large water changes, 20-30% weekly, can maintain parameters in lightly stocked or soft coral-only tanks. As your coral load increases, particularly once you're keeping multiple SPS colonies, consumption outpaces what water changes can realistically provide. Most SPS reefers with heavily stocked tanks find that large water changes alone are not sufficient and combine them with dosing.
Can I use a dosing pump for kalkwasser? Yes, but kalkwasser (calcium hydroxide) is caustic and precipitates easily if exposed to CO2. Most reefers use a peristaltic doser connected to a kalkwasser stirrer, which keeps the solution mixed and delivers it slowly as top-off water. The Avast Marine Kalk Stirrer is a popular pairing for this setup.
How many heads does my dosing pump need? A two-head pump handles basic two-part dosing. A four-head pump adds capacity for amino acids or trace elements. If you're running an advanced dosing protocol with multiple trace element supplements, an eight-head unit gives you room to grow. Start with four heads even if you only use two initially, so you have expansion capacity without buying a new pump later.
What's the difference between a dosing pump and an ATO? An Auto Top Off (ATO) system replaces evaporated freshwater to maintain salinity, typically using a gravity reservoir or a simple small pump triggered by a float switch or optical sensor. A dosing pump delivers precise, metered amounts of supplements on a timer. They serve different functions, and most serious reef tanks run both.
Keeping Your Reef Stable
A reef dosing pump is one of those pieces of equipment that makes the day-to-day reality of reef keeping much less stressful. Once you've dialed in your consumption rate, calibrated your pump, and verified your parameters are holding steady, you stop thinking about calcium and alkalinity and start enjoying your corals. The hardest part is the initial setup and calculation. After that, it runs in the background while your reef does its job.