In marine aquariums, available are several types of reactors. Reactors are simply acrylic cylinders that contain some type of media. Internal construction varies, depending on the brand and type of reactor.
What follows are reactor types and their purpose.
Perhaps the most valuable of the reactors in a reef aquarium is a Calcium Reactor.
Maintaining natural sea water levels of minerals and trace elements, and alkalinity of a sufficient level to buffer them, is a challenge for many new and not so new reef aquarium keepers.
A Calcium Reactor can negate that challenge. The reactor is loaded with an aragonite media or similar, which as it dissolves, continually maintains natural sea water levels of minerals and trace elements, and the optimal level of alkalinity. Having a Calcium Reactor is cost effective in the long run, since it will keep you from having to buy products for the marine minerals and trace elements, plus alkalinity, regularly.
What dissolves the aragonite is Carbon Dioxide (Co2). And that’s where the start-up costs climb. Though Calcium Reactors themselves are reasonably priced, needing only silicone tubing, you need a fully automatic Co2 system to run the reactor and that can be expensive.
A person will need a pH controller, a regulator, solenoid, needle valve and bubble counter, a Co2 cylinder, which you must either buy or lease, and find a place to get it filled. All told, even if you shop, you can expect to pay upwards of 400 US dollars for a fully automatic Co2 system
A fully automatic system is necessary because the life in your reef is accustomed to natural levels of minerals and trace elements. If a Calcium reactor was running constantly day and night, the life in your tank would suffer and many would die.
To set up fully automatic, you set the pH controller to an acidic pH, say 6.5. It has to be low enough to dissolve the aragonite media. If that pH drops below 6.5, the pH controller turns off the Co2 via the solenoid. It turns the system on if the pH rises above 6.5. In that way it adapts to the needs of your tank. Better quality Calcium reactors don’t allow any Co2 to escape them.
The dissolved aragonite drips into either a sump, or better, if your skimmer or skimmers have a John Guest port, you can route the line into the skimmer, mixing it far better than just dripping it into a sump.
The drip rate will take some tweaking, via the pH controller, until your tests verify the minerals and alkalinity are at natural sea water levels. Salifert has the highest quality test kits for marine parameters, and are what I recommend to reef hobbyists.
Though it is very rarely a problem in reef tanks, Nitrate can become one in fish only or fish only with live rock tanks. Nitrate Reactors can solve them.
The reactors are simply acrylic cylinders, usually with some sort of baffle to prevent media escape.
There are several media types for reducing Nitrate to zero constantly. All use a class of naturally occurring Nitrifying bacteria that oxidizes Nitrate, reducing it to Nitrogen gas.
First is plastic spheres within the reactor. Those bacteria must be fed regularly by a dilute alcohol solution.
Better is the spheres with feeding balls. The bacteria are fed until the feeding balls are consumed by them. Thus, the feeding balls must be replaced regularly.
The best media is Sulfur micro pellets. Though more commonly found in Germany, the Sulfur both feeds the bacteria and is their support. As it is a different type of Nitrifying bacteria in Sulfur Nitrate Reactors, they chemically reduce Nitrate to Nitrogen gas.
There are also several commercial products for Nitrate Reactors, but like others in this Nitrate Reactor list, they need to be replaced regularly, costing you money, while Sulphur pellets can be used for many years before needing replacement.
Sulfur reactor media can be found online if one searches. You can expect to pay around 40 dollars US for two pounds of it, less if you shop.
There are reactors available which can use different media, depending on the needs of the keeper’s reef aquarium.
High Phosphate can spur nuisance algae. There are many brands of Phosphate removal products. The best of them reduce it to the natural sea water level. Some lower quality products reduce it to zero, which is bad for the life in your tank.
Silicate in excess can also result in algae, and it can also stress corals, that in a worse case can cause tissue necrosis and death.
Products are available for media that removes excess Silicate down to the natural level. The best I know of removes both Phosphate and Silicate to natural levels; The Phosphate/Silicate Magnet, a Marc Wiess product.
Though there are reactors for varied media like that, one should remember that they need to be replaced when exhausted, which can become expensive in the long run.
These reactors usually need a low flow so the bacteria can work efficiently. All need a pump to move sea water into the reactor, and reactors usually come with a list of suitable pumps. Some better models come with the proper pump, media and tubing.
Reactors, as long as they are properly maintained, can be used for many, many years. The Calcium reactors I have were bought over 19 years ago, and still work perfectly.