This thread of mine discusses the mainstream methods for dosing alkalinity and calcium, including: two part dosing, calcium reactors , and kalkwasser/limewater as well as the effect of water changes.
http://www.reefcentral.com/forums/showthread.php?t=2447251&highlight=alkalinity
This is from it:
Caclium and alkalinity supplementation methods
<hr style="color:#FFFFFF; background-color:#FFFFFF" size="1"> Often folks seek advice on how to maintain calcium and alkalinity. It can be confusing. There are a number of informative articles by Randy Farley accessible via the sicky at the top of the Reef Chemistry Forum.
The following is a brief summary of the various dosing methods to help folks start to understand the options.
There are 3 mainstream methods which can be used independently or in combinations:
Two part dosing consists of dosing calcium chloride and carbonate in the same proportions as calcifying organisms ( coral, coraline, calms, etc) use them(50ppm/2.8dkh /1meq/l) carbonate alkainity to 20ppm calcium . Commercial mixes are often used and when dosed per instructions provide carbonate alk and calcium in those proortions. It is less expensive to use baking soda or soda ash/ baked baking soda for carbonate alkalinity and generic calcium chloride ;significantly so for larger systems with high demand but for smaller systems or those with low demand the commercial mixes may be more convenient. These supplements may be dosed manually or via dosing pumps. Either tha calcium part or the carbonate part can be dsoed separately to adjust alk or calcium independently.
Caclium reactors( CaCO3 reactors). Media consisting of coral skeleton and or other forms of aragonite is dissolved in acidic water in a fluidized reactor via the injection of CO2 which lowers the pH .The calcium and carbonate alkalinity are disassociated and provided to the tank where they are available for precipitation in the tanks higher pH water as calcium carbonate (skeletal mass) . Impurities / trace, minor and major elements stashed in the media are also dosed for better or worse depending on the actual contents of the media used. The pH of the dosed solution is usually around 6.5 to 7.0 ;so, it has a pH lowering effect on the tank water . Most tanks running on calcium reactors run with pH around 7.8 .
Limewater (calcium hydroxide;aka kalkwasser) provides carbonate alkalinity and calcium in the proportions used in the precipitation of calcium carbonate ( 50ppm carbonate alkalinity and 20ppm calcium) just like a balanced two part dose or the effluent from a calcium reactor. Limewater at full saturation ( 2 tsps of calcium hydroxide powder per gallon of fresh water ) has a ph of about 12.4. When it enters the tank the hydroxide binds with CO2 forming CO3 carbonate.This reduces CO2 while providing alkalinity( CO3) and raises the pH of the tank water. Limewater must be dosed slowly to avoid pH spikes which can lead to abiotic precipitation of the calcium hydroxide as calcium carbonate ,basically like coral sand.
I personally like limewater because of it's pH raising effect and it's self purifying nature .Many impurities precipitated out in the high pH limewater so the realtively pure calcium and hydroxide get to the tank.
I have used all three methods sometimes all at once. Many use limewater dosing along with a calcium reactor to balance off the low pH effluent from the calcium reactor.
With any of the three methods it is important to maintain magnesium as well.
