While frequent water changes and kalkwasser are sufficient for aquariums with low calcium and alkalinity demands, a fully stocked thriving reef tank will simply demand more.

A 2-part supplement, such as ESV B-Ionic, is a great way to maintain calcium and alkalinity. However, as your tank matures, it can become quite pricey and will require daily dosing. Joe from the Marine Depot staff, for example, has a 150 gallon reef aquarium and goes through roughly $400 worth of 2-part solution each year.

A calcium reactor is a more advanced method of maintaining calcium and alkalinity in a reef tank. It eliminates many of the common problems reefers experience using other methods. Intermediate and advanced hobbyists alike generally love the advantages a calcium reactor offers and achieve great success using them. However, for new hobbyists and even some intermediate reefers, setting up and operating a calcium reactor may seem intimidating.

This article and the accompanying video encompass part 1 of a 2-part series that will help demystify calcium reactors. We are going to explain how calcium reactors work, show you each of the individual components required to run a calcium reactor and hopefully ease some of the hesitation you may have so you'll feel more confident and motivated to automate your calcium and alkalinity supplementation.

Buying a calcium reactor does cost a lot more up front than other calc/alk supplementation techniques. The good news is that it is cheaper and easier to maintain in the long run. Once you have your calcium reactor dialed in, you simply need to check on it every week or so, refill the CO2 periodically and replace the calcium reactor media annually.

Another cool part about using a calcium reactor is that the media you are dissolving is actually composed of real coral fossils, so you are replenishing exactly what your corals need—and in the correct ratio. One of the biggest benefits of using a calcium reactor is that it will maintain much more steady levels of calcium and alkalinity, reducing the large swings commonly associated with dosing.

We've covered the benefits. Now let's talk about the gear you'll need to get a calcium reactor up and running.


Once you have acquired all the parts you'll need, you're just about ready to piece everything together. But first you'll need a solid understanding of the role each part plays before you dive in.

CO2 gas is needed to fill your CO2 bottle. You want food or medical-grade CO2. Restaurant supply and medical gas vendors can fill the CO2 tank for you.

A CO2 regulator attaches to the CO2 tank which allows you to precisely control the injection of CO2 so the proper pH level is maintained inside the reactor. The check valve is installed inline and prevents water from accidentally entering your regulator.

Injecting CO2 lowers the pH of the aquarium water inside the calcium reactor just enough to dissolve the calcium reactor media and enrich the water. This acidic water is enriched with calcium, carbonate alkalinity, strontium and trace elements. You can even mix in some magnesium media, like Brightwell NeoMag, to help maintain magnesium levels for you.

The calcium-rich acidic water is then slowly dripped back into your aquarium or sump. The feed pump is used to feed the calcium reactor with aquarium water. We often recommend the Tom Aquatics Aqua-Lifter because it is inexpensive and strong enough for most reactors working on a reef aquarium less than 250 gallons. Using a feed pump also makes it easier to dial in the outlet drip rate, called effluent. The calcium reactor itself also has a recirculation pump to recirculate water inside the reactor.

A pH test kit or pH monitor is used to measure the pH of the effluent solution before it is dripped back into your aquarium. This way you can ensure you are maintaining the proper pH inside your calcium reactor.  A pH controller (or full-fledged aquarium controller) is very useful for this job because you can actually attach it to the CO2 regulator with a solenoid and have it automatically control the output of CO2 to maintain proper pH. If the pH is too low, your media will turn into mush. If the pH is too high, the media will not dissolve.

Understanding how a calcium reactor works will really help you to properly operate and dial in the reactor settings for your tank. Follow the manufacturer instructions closely when assembling your calcium reactor and be careful when operating the CO2 regulator. Failure to do so can lead to some serious damage since the CO2 is under a high amount of pressure.

Next week we'll be back with part 2 in our 2-part calcium reactor series to demonstrate  how to dial in your calcium reactor settings and get it working properly. In the meantime, if you would like to learn more about calcium reactors, check out our calcium reactor diagram and this archived how to set up a calcium reactor article of ours on this topic.

If you found this article and/or the accompanying video helpful, please "like" and share them with your reef keeping buds considering a calcium reactor. Don't forget to subscribe to our YouTube channel so you can stay up-to-date on the latest hobby news and get expert advice from our staff.

If you have questions, leave us a comment below or contact us because we'd be happy to help you out. Until next time... take care and happy reef keeping!

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