Many reef aquarium hobbyists are equipment junkies. I know I am.

I love getting my hands on the latest gadgetry and hooking it up to my aquarium system. But with so many choices—from lights and protein skimmers to powerheads and controllers—it can sometimes be difficult to decide where to invest your money.

One of the first major investments I made in aquarium equipment (besides the tank itself) was purchasing a calcium reactor.

I had a 135-gallon mixed reef at the time with clams, LPS (mostly Euphyllia), Acropora and Monitpora corals. If I missed even a day of dosing with a two-part supplement, my calcium and alkalinity levels would drop. I constantly found myself playing catch-up and dosing more than usual. Vacations were out of the question.

The ever-increasing dosages my tank required had me forking over my hard earned dough for more and more bottles of two-part supplement.

There had to be a better way.

I did some research and, after speaking with several hobbyists about my situation, decided to purchase a calcium reactor.

The following is an excerpt from an article I wrote called Reactors and the Reef Aquarium:

Calcium Reactors

What You'll Need

The reactor itself, a feed pump (or small powerhead) to pull water from your tank or sump through the reactor, a CO2 regulator (preferably with a solenoid), a CO2 tank, a calcium based media and some flexible tubing (for hooking up the CO2 as well as the feed pump). A pH controller is also nice to use with a calcium reactor, but is not a necessity.

The Basics: How Calcium Reactors Work

Water is pumped (or gravity fed) from the main tank or sump into the calcium reactor where it is mixed with carbon dioxide (CO2). The mixing of CO2 with water causes a drop in the pH of the water. The lower pH allows the calcium-based media to dissolve, releasing calcium (and other elements) into the water. This calcium-enriched water (called the effluent) is then fed back into the sump or main tank to replenish calcium that has been utilized.

Reactors have a recirculation pump to help aid in the dissolving of the media within the reactor. This pump helps move water through the reactor more efficiently and allows the water to pass through the media multiple times before it is returned to the tank. This enriches the water with higher levels of calcium than if it were to flow only through the reactor once in a single passing. Some reactors are set up to push the water through the media from the top down (down flow), while others push the water up through the media (up flow or fluidized). I wouldn't get too hung up on deciding which would be “best” for your system; I have found both types work extremely well.

For this article, I'm going to set up my new toy, an AquaC RX-1 Calcium Reactor.

One of the many nice features about this reactor is that in most setups it doesn't need a feed pump. The recirculation pump creates enough of a pull to bring water in from the tank. In addition to the reactor, I have my Dual Gauge Regulator w/ solenoid10lb CO2 tank, KNOP Reactor Media and CO2 tubing.

I will be using an AquaController Jr. as a pH controller to shut off the flow of CO2 if the pH in the tank drops below acceptable levels. I won't go into details about how to setup a controller in this article but, if you have any questions, feel free to contact us. Tech support is always free.

First, I need to figure out where to place my reactor and CO2 tank/regulator. I don't have space underneath my sump, but I do have a remote refugium with enough space on the stand to place the reactor next to it. I also made sure there was plenty of space under the refugium stand for my CO2 tank to keep it hidden from site.

With the location found, I am now ready to get the reactor up and running. The first step is to fill the reactor with media. As mentioned, I will be using KNOP Reactor Media. I have used many types of media over the years and have been very happy with all of them, but have found the KNOP media tends to work best for my tanks. After rinsing the media to help eliminate dust (the dust can cause a temporary clouding of tank water, so I recommend rinsing it) I fill the reactor leaving a gap at the top. The gap helps prevent any chance of the media from being sucked into the intake and jamming the pump. If you needed to remove the reactor from its location to fill it with media, you can now return it back.

Now that the reactor and CO2 system are in place it is time to hook them together. It should be noted that it is very important to have a check valve between the reactor and the regulator to help prevent the back flow of water in the event the regulator is de-energized (power outage or if a controller turns it off). If your reactor did not include a check valve, you will need to purchase one before hooking up your reactor.

Using either the tubing provided or CO2 tubing, run the line from the regulator through the check valve and into the bubble counter on your reactor. Turning on the CO2 will be one of the last steps, so keep the valves turned off at this point.

I'm now ready to set up the inlet and outlet (effluent) lines. The inlet line should be positioned below the water line to pull water into the reactor. Avoid areas that are very turbulent as the microbubbles in these areas can get sucked into the reactor. The effluent line should be positioned at least an inch or two above the water line and it is OK to have this drip into a turbulent area. This can actually help to blow off any excess CO2 left in the water. I will be dripping my effluent into my refugium in hopes that any excess CO2 will be utilized by the algae in there. You will want to open the reactors effluent valve fully at this point.

It is time to start filling the reactor with tank water. If your reactor has a feed pump, you can turn it on. With the RX-1, I will need to manually fill the reactor with tank water. Once full, I will replace the cap and plug in the Eheim recirculation pump. This will get the water flowing through the reactor (pulling water in through the inlet line and dripping it out the effluent line).

Despite pre-rinsing the media, I will still end up with cloudy water within the reactor. But this will be a very mild cloudiness compared to if I hadn't rinsed it. To allow this to clear up, I will let the reactor run (still with no CO2 flowing) for around 5-10 minutes. By then everything should be clear. This is the perfect time to also make sure everything is running smoothly. Make sure there are no leaks in any of the fittings and that your effluent line and intake line are secure and running as planned.

Once the water has cleared you can adjust the flow coming out of the reactor. Different reactors will have different recommended flow rates, so you will want to follow their instructions at this point. I personally have found most of the reactors I have used work well with a flow rate of around 1-2 drips per second. A fellow hobbyist described the flow rate as a string of pearls. You will see individual drips, but they will be connected to each other (imagine a pearl necklace hanging down).

We are now at the last step. Start the flow of CO2 into the reactor. Like the effluent rate of your reactor, different manufacturers have different recommended bubble rates. Some (like the AquaC RX-1) have a recommended starting rate of 1 bubble per second while some others go as low as 1 bubble every 6 seconds. The flow rate of bubbles is adjusted by the needlevalve on your CO2 regulator. These valves allow for a precise control of flow out of the CO2 tank. Make sure you read over the instruction manual with your regulator and become familiar with how to set it up before using it.

You have successfully setup your reactor. From here you will just have to dial in the proper effluent rate and/or CO2 flow for your tank's needs. Testing your calcium and alkalinity levels over the next couple of weeks is very important.

Calcium Reactor FAQs

  1. Calcium reactors are best for maintaining the calcium levels in your aquarium. If the calcium levels in your aquarium are already low, you should assist your reactor by using a calcium supplement to raise the level and let the reactor maintain it from there. If you water is out of balance, a reactor won't solve this. This also holds true for your alkalinity levels. You will need to test them and make sure they are within acceptable levels. If they aren't you will need to adjust them as well. Your calcium levels should be maintained between 350-450 ppm and your alkalinity levels between 8-12 dKH.
  2. The calcium needs in your tank will change over time. As you add more corals and the corals themselves grow, you'll need to occasionally adjust your reactor. There are actually two adjustments you can make. The first adjustment is to increase or decrease the flow of CO2 into the reactor. The second adjustment is to increase or decrease the effluent rate. If you need to increase the amount of calcium being delivered to your tank, you would either increase the flow of CO2 (causing the pH to drop lower, dissolving the media quicker) OR decrease the effluent rate to allow longer contact time with the media. If you need to decrease the amount of calcium being delivered to your tank you do just the opposite. You will want to give time for the adjustments to work. Wait 24 hours before making more adjustments (and test your water).
  3. When first adding a calcium reactor to your tank, start with the manufacturer's recommended effluent and CO2 bubble rates for your size aquarium. Test your levels over the course of the next few weeks and adjust the CO2 bubble or effluent rate until your tank's desired calcium levels are sustained.
  4. Under normal usage, a 5 lb CO2 bottle lasts 6-12 months; media lasts approximately 6 months before needing to be replaced. While the initial investment of a calcium reactor may be a high, the long-term costs are very inexpensive. Not to mention the fact that you will no longer have to dose your tank on a daily basis with a two part supplement.
  5. Under the items needed I mentioned the use of a pH controller and at this time I would like to mention why this is a nice piece of equipment to use in combination with a calcium reactor. In a reef tank we are trying to maintain high pH levels (normally between 8.2-8.4). When using a calcium reactor we need to inject CO2 into the water to lower the pH to dissolve the media. Normally a well-balanced tank and a properly set up calcium reactor will have little to no effect on the pH of our tank. But if something becomes out of balance within the tank or there is some type of equipment failure that causes excessive amounts of CO2 to be injected into the tank, the pH in the tank could drop to dangerous levels. A pH controller monitors the pH level of the tank and can turn off the flow of CO2 by shutting off power to the solenoid on the regulator if the pH level drops below a set point. It is not suggested to use the controller as a means of turning the CO2 on/off on a daily basis, only in the event of an emergency (like the pH falling into the 6.0 range).

Hopefully this condensed version of how to set up a calcium reactor helped you setup your own or helped you decide whether a calcium reactor is right for you.

If you have any questions, please don't hesitate to contact us.