As we generally link reactors with nuclear reactors, the name ‘calcium reactor’ might seem quite scary if you’re not aware of them.

Well, it’s actually not that complicated. It’s a chamber that recirculates water and slowly dissolves calcium carbonate media.

Maintaining the water quality of reef aquariums is extremely important.

The calcium reactor helps to maintain the calcium and alkalinity level by slowly reintroducing the water back into the aquarium. These are the major water parameters for aquatic species such as stony corals, clams, etc.

The demand and need for calcium increase with the number of corals in the tank and this need grow even higher with fast-growing corals. In this article we will review a few of the best calcium reactors available in the market.

Our Top Picks At A Glance | Side by Side Comparison

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Why Should I Get a Calcium Reactor?

Best Calcium Reactor For Reef Aquarium

Calcium reactors help to constantly replenish the calcium and carbonate alkalinity that’s consumed by the critters in the reef tanks.

Marine critters like coralline algae, clamps, large polyp corals need calcium and carbonate ions to build their skeletons.

Hence, an optimum amount of carbonate and calcium should be present in the tank for the healthy growth of these critters.


Even though they are called calcium reactor, they also help to retain the alkalinity of the water. A calcium reactor helps to mix calcium and carbon dioxide to reduce the pH level of the aquarium water.

The initial investment on a calcium reactor is almost twice as higher compared to daily two parts dosing. However, the operational cost of a calcium reactor is much lower than the two-part dosing which eventually makes up for the initial investment.

A calcium reactor also possesses a lower chance of inducing carbonate precipitation in the aquarium pump and heaters compared to a lime water supplement.

Although, in aquariums without proper aeration, the pH level will run lower than regular. To bring back balance in pH, limewater supplement might be required as that will compensate for the pH drop.

How Does the Calcium Reactor Work?

The media gets dissolved as it slowly injects carbon dioxide in the chamber. As the carbon dioxide reacts with water, it produces carbonic acid. As the water starts to become acidic due to the presence of carbonic acid, the media starts to breakdown and starts releasing calcium and alkalinity into the water.

One of the best features of calcium reactor is that they very little maintenance once they are set up. Even if something goes wrong and the reactor stops working, it’ll not send off excessive carbonic acid to the tank water.

Our Top Picks of Calcium Reactors

  1. Reef Octopus VarioS CR140
  2. Viaaqua AC30 Acro-Cal Calcium Reactor
  3. Aqua Excel Calcium Reactor
  4. AquaMaxx cTech T-2 Calcium Reactor 

Top 4 Best Calcium Reactors Reviewed

1. Reef Octopus VarioS CR140

Reef Octopus VarioS CR140 5.5 inch Calcium Reactor

Reef Octopus offers a wide array of calcium reactors and the VarioS CR140 is one of the best they have to offer. Their calcium reactors range from small 50-gallon size to large public aquariums that can hold thousands of gallons of water.

These come in a single chamber with variable speed DC recirculation pumps. This reactor comes disassembled from the manufacturer. However, the assembling process is fairly easy and you’ll be done with the entire process in no time.

It comes with a reactor body with sponges and bracket, plumbing, recirculation pump, probe holder, O-ring seals and tubing with valves.

Make sure you never lift the reactor by the plumbing and never lift the reactor when it’s full of water. It comes with two years warranty for the pump motor and one year warranty on the reactor body.

Reasons to get
  • Can be used for aquariums up to 200-gallons
  • Variable speed
  • Easy to take off the lid
  • Apex ready VarioS 2 pump
Reasons to avoid
  • Expensive
  • Doesn’t come assembled from the manufacturer

2. Viaaqua AC30 Acro-Cal Calcium Reactor

Viaaqua AC30 Acro-Cal Calcium Reactor

The Viaaqua AC30 Acro-Cal Calcium Reactor has a small and compact design which is suitable for the reef tanks sized at 50-gallons to 200-gallons. Standing at a height of 22.75-inches and a width 5.5-inches, it provides the optimum amount of calcium required for the corals to thrive.

If you have a small tank, you might have a hard time equipping it inside the tank due to the height of the reactor. However, it can be placed in the aquarium or in the sump. It features a built-in water pump and a bleed valve. The control valve makes the adjustment processes easier to perform.

The sponge disc of this reactor ensures that aragonite media is stabilized and it provides an even flow distribution. You’ll also get a compression fitting so that you can equip a pH meter to regulate the flow of carbon dioxide in the reactor.

Reasons to get
  • Affordable
  • Control valve for the easier adjustment process
  • Comes with a buddle counter
  • Clear instruction manual guide
Reasons to avoid
  • Long height may act as a barrier to fit inside the tank

3. Aqua Excel Calcium Reactor

Aqua Excel Calcium Reactor

The Aqua Excel is another top of the line calcium reactor that will act as an absolute blessing for your coral reef tank. It has a compact size with a dimension of 7 x 11 x 23 inches and weighs only 13 pounds.

It effectively provides the corals with the optimum level of calcium so that they can thrive and maintain their alkalinity level. It comes with a Sicce Syncra 2.0 pump that includes 2 years warranty.

This calcium reactor is suitable for tanks sized up to 250-gallons. The height of the reactor may hinder it from placing it inside the tank, however, you can place in the sump or submerge in the tank if you have a large one.

There’s a bubble counter included with the reactor that helps to adjust the carbon dioxide. It also includes a pH probe holder where you can equip a pH meter to monitor the flow of carbon dioxide.

Reasons to get
  • Suitable for large reef tanks
  • Durable build quality
  • Comes with bubble counter and pH probe
  • 2-years warranty for the pump
Reasons to avoid
  • Slightly expensive

4. AquaMaxx cTech T-2 Calcium Reactor

Aquamaxx Ctech T 2 Calcium Reactor

The AquaMaxx cTech T-2 Calcium Reactor is a large calcium reactor that comes with an up-flow design where it mixes saltwater, carbon dioxide and carbonate inside the reaction chamber. This unique mixture effectively gets rid of the need for daily two-part dozing.

It’s made with high-quality cell-cast acrylic construction with an outstanding finish that’s made to last. The setup procedure is very simple and easy which will only take you a few minutes to perform the whole process.

This calcium reactor is quite large and it is suitable for tanks sized up to 500-gallons. It has high-quality inlet filter that helps to trap particulates while increasing the overall efficiency of the reactor.

The AquaMax comes with very simple maintenance procedures as it’s designed to ease up the works of aquarists. It also includes a pH probe for installing the pH monitor to have a look at the carbon dioxide level.

Reasons to get
  • Sturdy construction
  • Durable quality
  • Easy and simple setup procedures
  • Low maintenance
  • Accurate carbon dioxide bubble counter
  • Suitable for large tanks
Reasons to avoid
  • Not suitable for small tanks

The Important Features of a Calcium Reactor

The calcium reactor is not an excessively complex device. However, it comes with a number of equipments that need to be set up properly.


The material plays an important part in the durability and longevity of the product. Most calcium reactors are made with PVC piping. It’s very important that the acrylic has the optimum level of thickness otherwise the chamber walls wouldn’t be able to make a joint between the cylinder and flanges.


The calcium reactor consists of a chamber which is usually cylindrical in shape. This chamber holds the media and the pump which is used for re-circulating the water through the media. There’s a small valve which regulates the amount of water that will pass through the reactor and sometimes it incorporates a bubble counter that gives a visual indication of the carbon dioxide present there.

Water and carbon dioxide is then put in the recirculation pump inlet that mixes and feeds it back to the chamber to the water withdrawn from the chamber itself. The water then leaves the reactor through a small hose and it’s adjusted by a small valve to be returned to the aquarium.


The capacity of holding the media depends on the size of the chamber. The larger and taller the chamber, the more media capacity. The higher the size of the media the longer the media will be in contact with the acidic water. This will lead to more effective dissolution and carbon dioxide consumption.

Water Flow

Up-flow is the most popular flow kind for calcium reactors as they keep a clean space between the media grains. When the media flow, fine particles stay behind and eventually form a muddy texture that may plug the spaces between the grains. In an upward flow, the particles are channeled to the top of the reactor where they can exit with a proper flow rate.

Gas Pressure Regulator

The gas pressure regulator maintains a constant pressure and also acts as a dynamic valve at the delivery outlet regardless of the changes in flow. Most regulators come with two pressure gauges, the gauge which is closer to the connector measures the carbon dioxide pressure and the other one measures the delivery pressure.

Needle Valve

The needle valve is the manual miniature valve that makes small adjustments to the carbon dioxide flow. If you need to make small changes in the flow these stem-like needles make small changes when they’re turned.

Solenoid Valve

The solenoid valve opens and closes the supply of carbon dioxide using electricity. There are two main components of this valve: an electrical coil and the valve itself.

The valve is closed when it’s not powered. When power is supplied, the solenoid converts the electricity into a magnetic field that opens the valve.

pH controller

A pH controller is an electrical device that measures the pH inside the reactor chamber or recirculation loop. It helps to control the amount of carbon dioxide and helps to maintain a stable bubble rate.


The media of a calcium reactor can be two types. It can be either the pure calcium carbonate or old carbonate deposits from coral skeletons. The smaller media grains dissolve faster and it has a higher tendency to plug as it reduces the recirculation flow.

Additional Read: Best Aquarium Media Reactors

How to Set Up A Calcium Reactor

There are different ways to set up a calcium reactor but the easiest one consists of two steps:

  1. Get a stable concentration of Calcium and Alkalinity
  2. Adjust how much you dose to the tank

Watch the video to understand the steps properly –

Take help of the calcium reactor setup calculator and get yourself a good quality pH controller to keep the concentration stable.

Calcium Reactor Tuning with a Reef Tank Calculator

Once you setup the calcium reactor now it is time for fine tuning. Tuning is easy with the help of reef tank calculator. The same calculator we talked about in the previous section. Watch another video to understand the process properly –

Wrapping Up

Calcium reactors are not something you hear about every day and the name itself can be quite intimidating. However, they are extremely essential if you own a coral reef as they supply the calcium and alkalinity required for marine critters.

Making the initial investment can be quite intimidating as they don’t come cheap. However, they have a lot less maintenance cost which will make up for the investment. There are many calcium reactors in the market so choosing the right kind is also a hectic job.

In this article, we have reviewed the best calcium reactors in the market so that you can get the best one for your marine buddies to keep them healthy and enhance their growth.

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