I've been using a Precision Marine Kalk reactor to dose Kalk into my tank. However, I haven't been happy with the stirring pump mechanism. It uses a Maxi-Jet 400 that is inverted outside the reaction chamber. The issue is that the impeller tends to stick when inverted so the pump doesn't do what it should. I decided that I should just try and make my own since the fundamental mechanisms are fairly simple. First let's talk about what a Kalk Reactor is. I think the term "Reactor" is a bit misleading and makes people think that a Kalk Reactor is much more complex than it actually is. Per Dictionary.com: re·ac·tor (ree-ak-ter) A container, as a vat, for processes in which the substances involved undergo a chemical reaction. There really isn't a chemical reaction going on in a Kalk Reactor. It is simply a device which is used to automatically mix Kalk and water to create a saturated solution that will be dosed into the aquarium system. The key features of a Kalk Reactor are: - A way to get RO/DI water into the reactor. - An opening into which Kalk powder can be added. - A mechanism to periodically stir up the solution so that new RO/DI water and undissolved Kalk powder periodically mix such that the solution in the reactor is always saturated Kalk/water. - A way to get the Kalk/water solution into the aquarium system. - A way to see the bottom of the reactor so you know when to add more powder. Some features of those features: - New water should be added such that it goes to the bottom of the reactor where the undissolved Kalk powder will be. - Water should exit the reactor from the top. - The mixing mechanism should ideally take water from the top and push it to the bottom where the powder is. The PM Kalk Reactor I bought is a water-tight, sealed container. I'm not sure why. There really is no reason to have a sealed reactor. Instead, to make things simple, I decided to go with an overflow reactor. It is still enclosed, but not completely sealed. The image below shows the key components: - The reactor tube is 6" clear PVC. - The base is a flat bottom 6" PVC cap - The stirring pump is a Mag 2 - The top is a standard 6" screw-in plug - The stirring pump tube is 1/2" PVC that takes the output of the stirring pump and directs it to the bottom of the reaction chamber to a tee fitting that spreads it out two ways. First I drilled three holes in the clear PVC. Two for the pump and one for the drain. I used a 3/4" drill bit that is just smaller than the outside diameter of 1/2" PVC. I then used a grinder bit to open the holes just enough to insert PVC pipe through them. Lastly I gooped the crap out of the seams with PVC glue to seal them and hold them in place. I would rather find a better way to do this, but I currently don't know of one. This worked, but was a bit of a kludge. The image below shows the mostly assembled unit. The pump has unions inline so it can be replaced. For the water in, I used semi-rigid tubing and drilled a hole in the clear PVC just above the exit drain. I then pushed enough tubing into the reactor so that the tubing went to the bottom. I put the top on. This is where I will put in the Kalk powder. I wanted a top on the assembly so that stuff wouldn't fall in and evaporation would be minimized. Note that I did not glue this on. There is no reason to do so. Finally, I glued the base onto a 1" thick piece of PVC plate. This will give the whole unit a little more stability when standing. Back to the basics of a reactor: Water In: RO/DI water comes in via the semi-rigid tubing and enters at the bottom of the reactor. It is fed via a Bubble Magus dosing pump. Adding Kalk Powder: I unscrew the top of the reactor, add powder then screw it back on. Stirring Mechanism: The Mag 2 is on a timer to stir the reactor chamber 6 times per day for 30 seconds a pop. It take water from near the top of the chamber and pumps it to the bottom. Kalk into the Aquarium System: When RO/DI water is added,the system overflows into the sump. A Way to See the Bottom: The chamber is clear PVC. Questions: Why clear PVC instead of acrylic? PVC is far easier to work with. It isn't as clear, but it doesn't need to be. What would you do differently next time? Two things: First, as mentioned above, I would change the way I mount the pump tubes and drain tube to the reaction chamber. I'm not happy with what I did. I'm not sure yet how I would do that. Second, clear PVC is expensive. The entire reaction chamber doesn't need to be clear, only the bottom so you can see the undissolved kalk powder. To cut costs I would buy a one foot section of clear that would be on the bottom of the reactor then I'd get a 6" slip coupling to connect it to conventional PVC for the top x feet. Mine is three feet tall, it could be shorter.