There are many, many plans out there on how to build your own calcium reactor. Some are incredibly beautiful, some have all the bells and whistles, some are ratty looking, and some just plain don’t work. Well you are in luck; this one sits right in the middle of them all. It isn’t as beautiful as the best, although it is no pinto by any means. The beauty of this reactor lies in its simplicity, both in building and looks, and its use of off the counter parts. Also you need no special tools and about the only skills required to build it are knowing how to cut PVC and knowing how to tie your shoes; if you can not do this, please seek the nearest kindergarten teacher before continuing. Before I dive into the actual building process, I would like to discuss a little bit about the function and operation of a calcium reactor, and just simply how it all works.

Everyone knows that our tanks need calcium so our corals can grow and we can get those pretty little clumps of purple coralline algae. There a many different ways to meet the calcium needs of the tank; we have the typical bottled calcium liquid or powder, then we have the more advanced, but better, two part additives like B-ionic, and then kalk dosing, kalk reactors and calcium reactors. I am not going to discuss the pros and cons of each other than to say that a kalk reactor and a calcium reactor are far less maintenance once set-up, and keep the parameters very stable. So now that I have stood atop the soap box long enough, let’s get into the nitty-gritty of how a Ca reactor works.

The reactor itself is very simple. It is a large tube filled with some sort of aragonite media, ARM being an example and what I use. CO2 is slowly injected into the reactor in order to lower the pH of the reactor to a set point, somewhere in the mid 6 region, mine is set at 6.5. This can either be controlled by a controller, which I recommend, or by simply adjusting the bubble rate until you are able to reach the desired pH setting. The media slowly dissolves into the circulating water because of the low pH and the water becomes supersaturated with calcium and alkalinity inside of the reactor (My reactor Ca is around 550 with a DkH of 35). The reactor has an outlet that slowly drips water into the tank, this outlet is controlled by a small gate valve for precise tuning. A small pump, a maxi-jet or aqualifter, is used to provide the reactor with tank water to replace the saturated water that is being dosed back to the tank. There is also a larger pump used for circulation so that water is constantly being pumped through the media. That is how a Ca reactor works in a nutshell. One thing to be careful is to not over inject CO2 dropping the pH very low, then lowering your tank to levels deemed appropriate only for tetras and angelfish, the ugly freshwater kind. My counter to that though is that you would have to be incredibly stupid to dose that much CO2, it would require effort to be that stupid, and if you are in this category, you do not need to read any farther. Now that I have given my disclaimer, every one has to have one, we can move on.

I talked above about the simplicity of this reactor and I wasn’t kidding. Almost every part other than the pumps, the CO2 equipment and two small fittings, can be found at your local hardware store. Two versions of this reactor can be built: with a controller and without. I am going to include a parts list for both versions and tell you how to build both versions, there is really very little difference. So here is the parts list.

1. 3 x Feet of ¾” PVC
2. 1 x Foot of 1” PVC
3. 2 x ¾” 90 degree Slip x Slip PVC fittings
4. 2 x ¾” 90 degree Slip x Male threaded PVC fittings *(Only one needed if using controller)
5. 2 x 1” male threaded to ¾” female threaded adapters*(Only one needed if using controller)
6. 2 x ¾” unions (slip)
7. 2 x ¾” Ts slip, with the middle of the T being ½” female threaded *
8. 1 x ¾” T slip
9. 2 x ½” male threaded to ½” OD JG fittings
10. 1 x ½” male threaded to 1/4” OD JG fittings (believe that size is correct) fits standard airline tubing.
11. 2 x ½” to ½” threaded sprinkler rods (1” in length)
12. 2 x small rubber o-rings that will fit snuggly around sprinkler rods
13. 2 x ½” female threaded to ¾” slip PVC adapter
14. 1 x ½” female threaded to ¾” male threaded PVC adapter
15. 1 x 1 ½” slip to 1” slip PVC adapter
16. 1 x 3” slip to 1 ½” slip PVC adapter
17. 5 x feet ½” OD clear tubing (or however much you need for inlet and outlet tubing)
18. 1 x 1” slip adapter to ??? You need to play around with finding a fitting that is 1” slip on one end, and fits perfectly into the opening in the center of the underside of the lid of the filter. I know there is a fitting that fits perfect because I have it, I just don’t remember the size.
All of the above should be able to be purchased at Home Depot (HD)

19. Whirlpool whole house filter unit (clear) $55 at Lowes
20. Genx ps-pcgx-1000-nw http://www.customaquatic.com/customaquatic/subsubcategorypage.asp?subcatindexid=ps-ac-pm $18.99
21. Maxi-jet 400
22. 5 x feet CO2 resistant tubing (any online aquarium company)
23. CO2 Regulator (If using controller make sure its electronic, Milwaukee makes a nice controller/regulator combo) Ensure that your regulator has a bubble counter
24. CO2 Bottle (beveragefactory.com has some pretty cheap)
25. PVC Needle Valve Mcmaster.com Part #7781K42
26. Plastic screw to replace the metal screw in the burp fitting on the lid of the water filter housing

• If you can not find ¾” Ts with the ½” threaded, get 3 x regular ¾” slip and 3 x ¾:” slip to ½” female threaded adapters

Extra Parts Needed for using Controller
1. Probe Holder Mcmaster.com Part # 69915K56
2. 1 x ¾” T female fitting (HD)
3. 2 x ¾” Male to slip Adapter (HD)
4. 2 x 1” male threaded to ¾” slip adapter (HD)
5. pH Controller

• If you can not find ¾” Ts with the ½” threaded, get 3x regular ¾” slip and 3 x ¾:” slip to ½” threaded adapters

Now that we have all the equipment, it is time to get started by doing some modifications to the lid of the water filter housing. You will find a screw coming into the in side of the top that is metal and is used to burp any excess air out of the unit. If you want to keep this function, wish I would have, you need to find a plastid screw that will replace the metal screw. If you don’t want to keep this function, then just put a big glob of silicone over it. The next thing to do is to remove the ribs on the underside of the lid, they can trap CO2. You can use a dremel or whatever else you have laying around to accomplish this task. This takes care of all of the modifications that need to be done to the lid.


Before we move on we need to get a couple of things established to help make the directions more clear. I am going to refer to the front and back side of the reactor. There is no real front or back, so you are just going to have to pick a side as the front or back depending on how you want the plumbing run. If you want to see the plumbing like mine is, then the plumbing side will be the front side. Also my pictures have a few things that are different and have been changed to be more efficient in the design I am giving you guys. I have tried to annotate this on all the pictures where it is necessary. I hope that’s not to confusing.

Now we are going to start with the inside of the reactor. We are going to take our 3” to 1 ½” reducer and cut that down some. On the 3” side, we are going to cut it about a ¼” after it becomes flat and that will be the base of our standpipe. Next thing to do is drill lots of tiny holes through the cone section. These holes will be where your water comes out of, so make sure you have a lot, but don’t make them big enough that the media can fall through them. After that is finished we are going to glue our 1 ½” to 1” slip adapter into it. Now we have to do some measuring to find out exactly what length we need our 1” piece of PVC to be. We are going to place the standpipe base down into the filter housing and stick our 1”piece of PVC into that. Cut that pipe down to where it is sticking out the top of the filter housing about ½” or so. Now we are going to put our 1” fitting that fits into the filter housing lid. We now need to play around with cutting our 1” pipe down until you are able to screw the lid on perfectly tight and the standpipe goes into the lid of the reactor. Once you have that, glue the fitting onto your 1” PVC pipe and glue the PVC pipe into the base, and the standpipe is finished.



Lets move on now to setting up our pump to run externally. This pump says it is submergible only, but I have run it for a long time external with no problems at all. The inlet and the outlet of this pump are both ½” female threaded. We are going to take our ½” to ½” threaded sprinkler rods (1” in length) and glue them into the outlet and inlet of the pump. Then we are going to take the rubber O-rings and place them over the sprinkler rods and role them all the way down to the pump. I don’t know that these are necessary, but I believe in overkill. Now, on the outlet side of the pump, we are going to glue our ½” female threaded to ¾” slip PVC adapter. Try to get this snug against the O-ring. On the inlet side we are going to glue our ½” female threaded to ¾” male threaded PVC adapter. Now on top of the output of the pump, we are going to glue half of one of the ¾” slip unions. Your pump assembly is now complete.






With that task accomplished, we can get to work on assembling the unit. First thing is to glue the 1” male threaded to ¾” female threaded adapters into the filter housing on the “out” side. If you are going to be using a controller, screw in the 1” male threaded to ¾” slip adapter into the “in” side of the top, otherwise screw in the 1” male threaded to ¾” female threaded adapter. On the side that says out, we are going to glue in a 90 degree ¾” male threaded to slip elbow.. You need to screw it in as tight as possible but it must end up facing straight down. This is going to go down to the union on the outlet side of the pump that we just did. We need to cut a piece of ¾” PVC to the length from our elbow facing down to the top of the union. Ensure the pump and the water filter housing are on an even surface so that they sit exactly like they will when completed. Unfortunately, I never measured the exact length of PVC here so it will take a little trial and error on your part. Once you get this piece cut to the correct length, glue it into the elbow and the union. You now have the output part of your pump plumbed.

Our next step is going to be the outlet section. Let’s start up by the in section of the filter housing top. We have already installed our 1” to ¾” adapter. If you are not using a controller, screw in a ¾” male threaded to slip 90 degree elbow. Tighten this down but you want this to end up facing the front of the reactor, parallel to the ground. If you are not using a controller, skip to the next paragraph. If you are going to be using a controller, then you need to install a 2” long piece of ¾” PVC. Take your ¾” slip T fitting and on one of the longer ends, install a ¾” slip to ½” female threaded adapter. Now glue the T fitting onto the 2” long piece of PVC that we glued into the top of the filter housing (The T should end up being parallel with the ground and the side that we just installed the adapter on should face the back of the reactor and the open end should face the front side of the reactor.



We are going to cut a 2” in length ¾” PVC pipe and glue that into the elbow or the T fitting. On the end of this, we are going to glue our other ¾” union. We now need to do some other construction to get things ready. Get the 3 Ts with the ½” female threaded side together. In two of them, we are going to screw in and glue our ½” OD JG fittings and then screw in the ¼” OD JG fitting into the third T. In the third T we also need to glue in a ¾” slip to ½” female threaded adapter. Between the two Ts, we are going to glue a 3” in length piece of ¾” piece of PVC. You want to try to line the JG fittings up as best as possible.


Now we are all on the same page, so we can move forward together. We are going to work back over on the pump side of the reactor. One the inlet of the pipe we are going to screw in our ¾” T that has the ¼” OD JG fitting onto our pump. You want to end up with the JG fitting pointing straight up, you can do it at any angle, but this is the easiest to work with later. We are almost done with the outer assembly, but we are at the tricky part now.

We have to get the piping from the pump side T to the exact distance sticking out of the pipe from the top of the reactor on the other side. So you need to take whatever length PVC and glue them into the Union and the T so that they are equal. On the end of both of those you are going to glue an elbow so that they are facing each other exactly. The best way to do this is mock this whole section up before you glue anything. What you need to do is take your Ts with the JG fitting that are glued together and find the right amount of PVC to go on either end of your Ts to those elbows so that everything goes together really smooth. Once you have this accomplished you are ready to glue this section together. I would suggest pointing both of your JG fitting down that way when water is coming out of the reactor, the CO2 will be at the top of the piping and it won’t come out and go into your tank. Now glue everything together and you have the main part of the reactor built.


Now we need to take our MJ 400 and attack the ½” OD tubing to the output of the pump. You don’t need to glue this on, it will hold tight. This hose is going to go to the lower of the 2 JG fittings on the long part of the plumbing on the front of the reactor. The hose needs to be long enough to go from your sump to your reactor. The other JG fitting is going to be for our outlet back to the tank. Go ahead and put a 6” piece of ½” OD tubing into this fitting. On the end of the tubing, put our plastic gate valve into the tubing. Then cut a piece of tubing long enough to go from the gate valve to your sump and put it onto the gate valve. The other JG fitting is going to be where we will be pumping CO2 into the reactor. The only thing we have left to do is test everything out looking for leaks. For testing purpose, tie off on end of some airline tubing and insert the other end into the CO2 inlet on the reactor.

Fill the filter housing with water and screw it in tight to the lid. We are now ready to test everything out and look for leaks. Make sure you put your standpipe in for the test as well. If you have a reactor that is going to use the controller, you can screw your pH probe into the holder, or else a sharpie fits in there nicely, we just need to block that hole so we can fill everything up and test the reactor. I would sit the reactor on the counter and fill you sink up with some water. Place the MJ 400 in the sink and plug it in. This should start filling up the reactor. Ensure at this point the outlet tubing of the reactor is going back into the sink; we don’t want to flood the kitchen. After it gets as full as it can, plug in the Genx pump to start the recirculation of the water inside the chamber. Open the gate valve on the outlet side all the way up. It will take about 5 minutes to clear all of the air out of the tubing, but that is not a big deal. Just let it run for a while and watch for links. If you replaced the screw with the plastic one in the lid, you can try burping the reactor to clear the air out quicker. I don’t know how well this works because I didn’t save this feature on mine. If everything looks good and you have no leaks, give yourself a pat on the back, you now have a working calcium reactor. If you still have leaks, get those fixed and test again.

Note for those who have a controller. When inserting the pH probe, do not insert it very far or it will greatly reduce the flow of the reactor. It only needs to be in there about ¾”.

Before we set up the reactor on the tank, you need to check your alkalinity and calcium levels of the tank. If they are not where you want them, you need to get them fixed before we hook the reactor up. The reactors job is to maintain levels, not raise them.

After you have a leak free reactor, it is time to get it going on the tank. Wash your media thoroughly in some water to remove all the dust. Some people say you should soak it for a week in RO water, but I never have and have had no ill effects. Fill the reactor up with media up to 1” below the top of the filter housing. You can also add some dolomite or Zeo-mag if you want to use the reactor to help maintain your Mg levels also. If you decide to do this, follow manufactures guidelines on how much to use. Fill the filter housing with tank water until it is almost full. Screw the filter back into the lid and ensure the standpipe is sitting snugly into the lid. Place your reactor wherever it is going to reside and get your inlet and outlet hoses hooked up. Now we are going to put our CO2 line into the reactor. Ensure now that if you are using a controller, the pH probe is inserted into the reactor tightly, but not inserted far enough to impede flow. Start filling up the reactor and when it is full, plug in the recirculation pump. Once we get all the air out of the reactor and are happy with how everything is looking, we are ready to start dosing CO2.

First thing to do is close the gate valve on the outlet side. Now you start dripping CO2 to lower the pH of the reactor. I would run the CO2 wide open for about 20 seconds to give you a head start. After you do this, slow it down to where you are reading about 30 bubbles per minute in your bubble counter. We are going to continue dosing CO2 until we get to our desired pH level, I would start with around 6.7 or so. You don’t want to get lower than 6.4 with ARM or it will turn to mush in time. If you are using a controller, set it at 6.7 and walk away until you see that the pH has gotten there. If you are not using a controller, every few minutes you will have to test the pH off the effluent until we reach the desired level. Once we get there, it is time to start dripping effluent into the tank.

Open your gate valve up so that it is dripping about once every second to every two seconds. Give this about 5 minutes and then check the pH and make sure it is stable. You will have to adjust the bubble count per minute of your CO2 until you get a stable pH reading with your effluent. Once you have made sure that your effluent pH is staying constant, you need to let it sit for a day or two.

Now you begin the process of tuning the reactor to your tank. This part can be a real pain. After a it has been running a day or two, you need to check your tanks alk and Ca. If they have lowered from where you want them, then you need to either increase your effluent rate or lower then pH in the reactor by dosing more CO2. Either of these will help to have the effect of dosing more alk and Ca to your tank. If you increase your effluent rate, you need to ensure the pH does not rise in the reactor, if it does, you will have to add a little more CO2. It will take a couple of weeks of adjustments before you get everything perfectly balanced, but once you do, it will be good to go for a couple months at a time. For the first month or so check your Ca and alkalinity levels every couple of days to make sure they are staying where you want them, then after that you will only need to check them once a week or so.

Congratulations, you now have a working Ca reactor that you can take pride in knowing you built it all yourself. If you ever have any questions you can contact me at jbjones@smu.edu.

I would like to give credit where it is due. The initial design of this reactor was created by WMTasker on RC and improved upon by myself and others. It is through the efforts of many people that this reactor came to be what it is today.