Calcium Reactors (CR) are an essential component to SPS systems and helpful in soft corals systems. There are several important components to consider

CO2 CYLINDERS

These are the containers that look like a scuba diving tank. You can purchase one from a local airgas supplier that provides CO2 to the restaurant industry. The CO2 that you use to dissolve your aragonite in your CR is the same gas that they use to give the fizz to your soft drink (aka sugar water) . You will need to get this refilled periodically, as the gas is used up. However if you have a leak, you can use up the cylinder very quickly. That's why we recommend that you make a solution of water and liquid soap and apply this all fittings on the CR assembly. If there is a gas leak, it will form a bubble, and you can pinpoint the leak and fix it.

AIRLINE

Make sure that the airline you use for the CO2 is made for it. Otherwise, the gas can leak out of regular airline tubing.

FLOW METERS

The biggest challenge we have found in CR Accessories is getting a flowmeter to accurately control the flow of the CO2 (carbon dioxide) from the CO2 tank to the calcium reactor.

It is quite difficult to maintain a very slow flowrate in most meters, as even at their smallest setting, they allow too much CO2 throught.

Once you find a meter in the proper range, adjusting its needle valve properly is difficult and often times they clog up the stuff and quit working. Sometimes they will allow too much CO2 into the system, which can also be a disaster if left unattended for long.

So we are not happy with any of them yet. We are still in process of looking for great CO2 valve and maybe someone will contact us and recommend an excellent one, which we will then post here.

AUTOMATIC CUTOFF VALVE

Usually when you buy a package for a CO2 system, it will come with an AUTOMATIC CUTOFF VALVE. The purpose of this valve is to cut off the flow of CO2 to reactor to your reactor when the power goes out. This is necessary because CO2 is pressure fed without using electricity at all, but the rest of the CR uses electricity to function. So if the power goes out, the CO2 is still flowing to your CR and then to your aquarium. Not good. This can rapidly lower your pH in the aquarium causing all sorts of problems.

The cutoff valve will cut off the flow of CO2 to the aquarium when the power goes out. So be sure to get one for your CR

When you choose a CR, make sure that it is easy to clean! We bought some in the early years from a German supplier and even though they work okay, the maintenance on them is an incredible chore. If we want to "punish" one of our workings, the running joke is they have to clean one of the calcium reactors!

We had to fabricate special tools to reach down to the bottom and to clean out the two lines inside the reactor which clog up all of the time. So it is a huge headache to maintain these and I silently curse the manufacturer each time I have to clean one. We have too many of them to replace them all, but as new systems come online, we are careful to choose CR models that will be easy to clean and maintain. So you should too!

To make sure that the model you are buying is easy to maintain, and the best way to find out which make and model works really well, you should checkout a bulletin board like ReefCentral.com
where people talk about different types of equipment. I think it's the it's important get unbiased opinions from people NOT trying to sell you their product.

Plus we use primarily commercial equipment anyway, so we cannot really recommend specific equipment for hobbyists.