The feed pump for a calcium reactor is a small peristaltic or circulation pump that delivers aquarium water into the reactor at a controlled, steady rate. Without it, your calcium reactor either runs dry or floods unpredictably. The feed pump controls how much water passes through the calcium reactor media per hour, which directly determines your calcium and alkalinity output. Get the flow rate right and your reactor runs efficiently. Get it wrong and you'll chase pH swings or have media that dissolves too fast.

Most reefers use a dedicated small pump set to deliver between 10-50 milliliters per minute into the reactor, though the exact rate depends on your tank size, coral load, and the specific reactor you're running. This guide covers how feed pumps work in the system, what flow rates to target, which pumps are worth using, and how to dial everything in without constantly adjusting.

What a Feed Pump Actually Does in a Calcium Reactor System

A calcium reactor dissolves calcium carbonate media (usually aragonite or coral gravel) using CO2 to acidify the water inside the chamber. The acidified water dissolves the media, releasing calcium and carbonate ions back into your display tank.

The feed pump is responsible for pulling water from your sump into the reactor. The water moves through the media chamber, picks up the dissolved minerals, and then exits through the effluent line back into the sump. The feed pump sets the residence time of water inside the reactor. Slower feed = longer contact time = more dissolution per pass. Faster feed = higher volume output but lower concentration per pass.

Why Feed Rate Matters for pH

When CO2 is injected into the reactor chamber, the chamber pH drops to around 6.5-6.8. That low pH is what drives dissolution. If the feed pump runs too fast, water moves through the chamber before CO2 can drop the pH low enough, and the media doesn't dissolve efficiently. If the feed pump runs too slow, the chamber pH can drop below 6.5, over-dissolving the media and crashing the effluent alkalinity.

The goal is to hit a stable effluent pH of around 6.5-6.7 and an effluent alkalinity of 25-50 dKH, then adjust your effluent flow rate (a separate needle valve or secondary pump) to hit your tank's consumption target.

Peristaltic Pumps

Peristaltic pumps are the gold standard for calcium reactor feed applications. They use a rotating mechanism to squeeze flexible tubing, moving precise volumes of liquid without the pump internals touching the fluid. This means zero contact with calcium-laden water, minimal fouling, and extremely consistent flow rates.

The Kamoer FX-STP2 is a popular choice. It runs at 0.1-50 mL/min adjustable, connects to a controller, and costs around $60-80. The BRS Dosing Pump also works well in this role, especially if you're already using the BRS dosing system for two-part. Just run a dedicated pump head for reactor feed.

The main disadvantage of peristaltic pumps is that the tubing needs replacement every 6-12 months as it wears. Budget about $5-10 per year for tubing.

Small Powerheads and Circulation Pumps

Some reefers use a small powerhead (like the Maxi-Jet 600 or a Rio Plus 180) with a ball valve to throttle down the flow. This works, but precise control is harder to achieve. A 180 GPH powerhead throttled down to 30 mL/min is fighting against its own pressure, which can make flow rates inconsistent as the valve position shifts with vibration.

If you go the powerhead route, use a needle valve instead of a ball valve for finer control. The BRS needle valve ($15-20) paired with a small Rio pump can work reasonably well for a single-stage reactor.

Dedicated Reactor Feed Pumps

Reef Octopus and Two Little Fishies both sell reactors bundled with purpose-built feed pumps. The Two Little Fishies Kalkwasser/Calcium Reactor Combo uses a small 9V DC circulation pump rated at about 15-30 GPH, which is overkill but easy to throttle. If you're buying a new reactor, check whether it comes with a recommended or bundled feed pump before buying one separately.

Sizing the Feed Pump for Your Reactor

There is no single correct flow rate. It depends on your reactor chamber size and the CO2 injection rate. Here's a practical starting point:

  • Small reactors (like the Deltec PF509 or similar 2-liter reactors): 20-40 mL/min feed rate
  • Medium reactors (5-liter, like the Reef Octopus CR-140): 30-60 mL/min feed rate
  • Large reactors (10+ liters, for systems over 200 gallons): 50-120 mL/min feed rate

The best approach is to start at the lower end of the range, measure your effluent pH and dKH after 24 hours of stabilization, and adjust from there. You want effluent pH around 6.5-6.7 and effluent dKH high enough that you don't need to run excessive effluent volume.

Setting Up Your Feed Pump

The feed pump typically pulls from your sump, below the water line, through 3/8" or 1/4" tubing into the reactor's inlet. Positioning matters: place the pump intake away from the return pump and skimmer to avoid pulling in microbubbles.

Run the tubing with a slight downward slope from sump to pump, and from pump to reactor. Air pockets in the tubing disrupt flow consistency. A simple union or check valve between the pump and reactor prevents backflow if the pump loses power.

For controllers, some reefers connect their feed pump to an Apex or GHL controller to automatically pause it during top-off events or other maintenance windows. This prevents the reactor from running dry during a planned water change.

If you're still selecting your reactor, check out our Best Calcium Reactor for Reef Tank guide for complete system recommendations, and our Best Co2 Regulator for Calcium Reactor article for the CO2 side of the equation.

Troubleshooting Feed Pump Problems

Inconsistent Effluent Output

If your effluent dKH swings up and down, the most common causes are: air in the feed line (check all fittings for small leaks), a worn peristaltic tube causing inconsistent compression, or a partially clogged inlet strainer.

Pull the tubing, blow it clear, check the pump head for wear, and clean the inlet strainer. Most feed pump issues trace back to these three things.

Reactor Chamber Running Dry

If the chamber is running dry, the feed rate is too low relative to effluent output. Either increase the feed pump rate or reduce the effluent flow. If the pump is already at max output, check whether the effluent needle valve has drifted open.

Media Dissolving Too Fast

If you're going through media faster than expected, the chamber pH is probably too low. Either reduce CO2 injection rate or increase the feed pump rate to raise chamber pH slightly. Target 6.5-6.7 for optimal dissolution rate.

FAQ

Can I use the same pump for feeding a calcium reactor and dosing two-part? No. Two-part dosing and calcium reactor feed are separate systems with different requirements. Two-part pumps dose precise small volumes on a schedule. A calcium reactor feed pump runs continuously at a steady low rate. They serve different purposes and shouldn't share the same pump.

What tubing should I use with a peristaltic feed pump? Silicone tubing is the standard. It's flexible, non-reactive with saltwater, and compresses consistently. Most peristaltic pump manufacturers specify tubing OD and wall thickness for their pump head, so match those specs exactly. Using the wrong diameter causes inconsistent flow.

How often should I check my calcium reactor effluent parameters? Weekly when first dialing in the system. Once stable, monthly checks are enough. Measure effluent pH with a calibrated probe, effluent dKH with a titration kit (not strips), and verify tank calcium and alkalinity haven't shifted more than 10% from target.

Do I need a feed pump if my calcium reactor has a recirculating pump? Yes. The recirculating pump circulates water internally between the reactor chambers for better CO2 contact. The feed pump is a separate component that moves fresh sump water into the reactor and pushes effluent out. These are two different pumps with two different jobs. Most good reactors use both.

Key Takeaways

A peristaltic pump is the most reliable choice for calcium reactor feed duty. Start at 20-40 mL/min for smaller reactors and dial up from there based on effluent pH and dKH measurements. Keep the feed line free of air, replace peristaltic tubing annually, and position the inlet away from skimmer turbulence. Once dialed in, a calcium reactor with a quality feed pump holds parameters more steadily than two-part dosing and costs less per gallon of capacity over time.