Currently there are three main ways to maintain Ca/alk levels in the reef aquarium:
1...Calcium Reactor
2...Nilsen/Kalk reactor
3...two part supplement
If you live near the ocean and have access to clean Natural Sea Water, thats a fourth option, but its not really feasible for you and I here in the midwest.
There are loads of plans on the internet for DIY Nilsen/Kalk reactors and Calcium Reactors if money is an issue. I've never built them, so I cant comment on what design is easiest or most efficient.
To run a calcium reactor you will need a minimum of a reactor itself, a CO2 tank, and a regulator w/ solenoid and needlevalve. If your reactor does not come with a bubble counter, you will need one of those as well. It is a good idea to have a pH monitor at least as well, but not necessary. I dont run my system with one. All of these items will run you somewhere in the vicinity of $400 -$500 if buying new, substantially less if buying used or DIY'ing the reactor itself.
A calcium reactor is just a tube or container that holds some form of caclium aragonite based media that will release calcium when dissolved. The CO2 will lower the pH of the water in the container to a point where the media dissolves, thus releasing the calcium and stabilizing Alk. The needlevalve allows you to adjust the CO2 rate. Too much CO2 and your media will dissolve too quickly and turn into mush. Too little CO2 and your media wont dissolve at all. The solenoid is eletrically governed. No electricity, it blocks CO2 from being released into the reactor. This keeps it from constantly dumping co2 in the event of a power outtage.
Nilsen/Kalk reactors drip Kalkwasser at a set rate into the tank. They are a tube that is filled with RO water and calcium hydroxide, (Kalk). There is some sort of stirring device, (rotating bar, rotating magnet, or power head) that keeps the kalk in suspension, and a peristaltic feed pump of somesort is connected to an RO supply and kalk is introduced to the tank this way. I would ABSOLUTELY consider and pH controller to be manditory with this set up. I have read waaaaaaayyy too many horror stories of something going wrong and too much kalk is introduced to the tank nuking everything. Kalk has a pH of somewhere around 12. It doesnt take much to wipe out a tank. a pH controller will shut down the reactor if pH reaches a certain end point. Another fun fact of kalk is that it will leave a residue on pumps and powerheads that will need to be cleaned off about every 6 months or it will wear out your pumps faster. They are cheaper than calcium reactor set ups though. Some large systems use both calcium and kalk reactors to maintain Calcium, Alk, and pH levels.
Two part...you will need the two parts being used...you can buy a pump of sorts that works on an air pump and a timer to dose the two parts at a set time daily. This is the least expensive up front, but as mentioned earlier, will cost the most over the long haul. It is also the most maintenance intensive way on your part.
Calcium reactors cost more up front but are the easiest and least maintenance requireing way to do this.
Just somethings to think about.
Nick
