What is a calcium reactor?  How do I set one up?

Calcium reactors are a simple piece of equipment, but for many people they can initially appear intimidating.

The basic function of a calcium reactor is to add carbonates into salt water. When keeping a reef tank with invertebrates and hard corals, levels of calcium and alkalinity will often be depleted very quickly. A calcium reactor is a capable and highly cost effective method of continually replenishing carbonate levels.

A calcium reactor is simply a plastic tube filled with media, often graded coral gravel. There’s a re-circulation pump to move the water around within the tube and through the media. There’s three main small bore pipes, one for water in, one for water out and, one for gas in. The reactors work by using co2 gas to drop the ph within the reactor, to about ph 6.5, this slightly acidic fluid slowly dissolves the media, liberating the carbonates and minerals within the coral gravel.

You will also need to buy co2 regulators to fit bottles of gas and the media for the calcium reactor. You may also choose to buy an adjustable flow dosing pump and a ph controller.

Achieving the correct PH within the reactor

There’s a few ways to run a reactor and supply the correct amount of gas.

If you don’t want to use a ph controller you can very simply use this as a starting guide – for every 50ml of water outputted of the reactor each minute, will require about 25 bubbles of co2 per minute. To test if this is working, you should use an alkalinity test kit and measure the reactors output, you want to achieve about 30-40 dkh on the enriched output. Most alkalinity test kits wont read this high, so I suggest you dilute the water, one part reactor water to 3 parts reverse osmosis water, then multiply your test result by four.  If your dkh is too low on the reactor output, slightly increase the amount of co2 being introduced. It’s important to use a stop watch and an accurate measuring cylinder with millilitre measurements – do not guess it!

If you’re reactor is not meeting the demands of your corals, then you can simply increase the water input and gas input accordingly, so if you started off with 50ml of water per minute and 25 bubbles of co2 per minute, then you may choose to increase to 60ml of water per minute and (you guessed it) 30 bubbles of co2 per minute.

A lot of people choose to use a ph controller with a co2 solenoid. With a ph controller, you have a ph probe that measures the water in the reactor. The probe instructs the controller to open or close the co2 solenoid, so that the correct amount of co2 is added to achieve your desired ph value at all times. So all you’re left to do is feed water to the reactor, so if your carbonates are too low, you simple push more water through the reactor – the ph controller takes care of co2 addition. Conversely if your carbonate levels within the tank are too high, you simple supply less water to the reactor and again, the ph controller will reduce the amount of co2 addition.

For supplying water to the calcium reactor, some people either t-off their sump return pump or other people may choose to use a dedicated adjustable flow peri pump, to very accurately supply and precisely adjust water flow rates.