A little Chemistry: Back to Basics

Calcium levels in the sea and in our aquaria are dependant on several factors. These are:

CO2 levels
PH
Alkalinity
availabilty of required elements
Carbon dioxide , when mixed with water forms a weak acid called Carbonic Acid. Obviously this has a low PH. When this acid comes in contact with the required element of Calcium in the form of aragonite or other calcerous gravel, it has the effect of dissolving it and allowing the components to go into sollution. This is the basis for most of the methods of Calcium additions to our tanks.

The following equations describes what happens when we mix calcium Hydroxide with water

(1) Ca(OH)2+H2O<-> Ca2+2OH- + H2O
Calcuim Hydroxide and Water form a saturated solution called Kalkwasser or Lime water. This solution has a very high PH around 12. When adding Kalkwasser one has to be careful about not raising the PH of the tank water too high or too quickly. CO2 used in conjuction with Kalkwasser will help to prevent this from happening.

This equation represents what happens when CO2 is added to the water:

(2) CO2 + H2O <--> H2CO3<--> H+ + HCO3- <--> 2H+ + CO32-
This reaction shows that when CO2 is added to seawater both Hydrogen carbonate and carbonates are added. When you use both methods the tank water is provided with Calcium and Carbonate ions together. Unfortunately only a small amount of Calcium will be added by using Kalkwasser alone because you are limited by its high PH for one ,if you do not inject CO2 and because you can only use kalkwasser to refill the water lost to evaporation.However there are ways around this dilemma.

Methods:
Various methods exists for the addition of Calcium. The first we will discuss is Kalkwasser. Kalkwasser is made by mixing Calcium Hydroxide and RO/DI water. The clear solution that is made is used to replace all evaporated water from the tank. This method is cheap and simple. However the Kalkwasser must be dripped in at a slow rate preferably during the nightitme hours. This helps to keep the PH up during the night when due to respiration of the inhabitants the trend is for the PH to go down. A simple method for dosing is to use a float valve that automatically lets down the correct amount of fluid to compensate for evaporation. This method will dispense Kalkwasser all day at a constant rate. The only disadvantages are that the float valve will have to been cleaned periodically to maintain a steady drip. About one evry two months a vinegar bath might be needed in order to dissovle calcium deposits on the valve that will clog it.

Another method for Kalkwwasser dosing is to use a float switch. This is different froma float valve. The float switch will sense that the water is low in the sump and will send a signal to a pump which will dose the Kalkwasser. A large reservoir holds the kalkwasser. Remeber to keep the reservoir tightly closed to prevent the kalkwasser from losing its potency. One disadvantage of this method is the potential for the pump to clog due to calcium deposits. One can improve on this method by using two reservoirs.

Aquarists wishing to avoid the dangers involved with the use of Kalkwasser have turned to using commercially available supplements to dose calcium. Some of the one part mixtures are solutions of Calcium Chloride and water. Calcium Chloride is prefered by some because of its ability to dissolve large quantities of calcium into the water at one shot. At first this would seem to be a good thing but every good always has a downside. Over time the addition of Calcium Chloride has the effect of producing an imbalance of chloride ions in the water. Water changes will not be able to fully compensate for this inbalance. As such,in my opinion Calcium Chloride addtions should only be used for periodically raising the calcium levels not as a maintenance procedure. Kalkwasser is the prefered method for maintaining levels constant.

Some two part supplements have recently been introduced to the market. One such supplements is called B-Ionic Calcium. This product claims to adjust both the Calcium level and alkalinity of the tank. The company that markets the product, ESV inc. of New York and the developerof the product,Bob Stark have stated that their product is a balanced ion calcium and buffer solution.They advise that this supllement will also raise the salinity of a tank because it is composed of chemical salts. They reccommend changing some of the water in the tank per month. I have used this product extensively on one of my test tanks and have found it to work as advertised. However the cost of the product over time is a slight disadvantage to its use. The two solutions must be used in equal parts every dayand testing should determine the dosage . For small systems with low evaporation rates this product is ideal. For larger systems this supplement along with the use of Kalkwasser is reccommended.

Some companies like MTC of New Jersey also make a lime doser called the Prolime. This clever device allows one to dose Kalkwasser at timed intervals. One can also control the rate of addtion as well as the exact dosage. The cost is not too high and setup and maintenance are not too complicated or labor intensive.The quality of the product is also first rate as are all their products..

In my opinion, Calcium reactors are excellent equipment to have if one can afford the cost of the intial setup. They will improve the conditions in the tank as well as cut down some of the chores involved with the making and dosing of Calcium solutions. They are not for everybody. The technical side of these products is something you must feel comfortable with before investing your money on a system. If you are running small aquaria with little evaporation then one of the commercially available calcium dosing supllements are your best choice. An all around best choice is kalkwasser. It is a cheap method although it does have some risk associated with it. An alternative to using Calcium hydroxide from a petshop is to use pickling lime from a grocery store. It is food grade Calcium Hydroxide and is relatively inexpensive. Be carfeul around children and when handling this substance. Calcium reactors are the best choice if you have a large number of calcium depleting organisms such as SPS corals and clams in your aquaria. The increased availabilty of Hydrogen carbonates and carbonates will have a profound influence on there growth rate.