Hi,
Some kalk reactors from Germany inject CO2 into kalk. It works both ways.
Ca(OH)2 + H20 <=> Ca++ + 2OH- + H20
CO2 + H20 <=> H+ + HCO3-
So
Ca(OH)2 + 2H2O + 2CO2 <=> Ca++ + (2OH- + 2H+) + 2HCO3-
So what does all that mean. Well, Ca(OH)2 or kalk, by itself adds Ca++ or ionic calcium to the solution. Also, it adds an OH- or hydroxide or pH increasing agent to the water. If we don't add anything else to the water, the OH- concentrations we get so high that we have a pH of 11 in our reef tanks. Obviously, something else happens before the pH reaches 11.
CO2 is always present in our tanks and it has a negative pH contribution (i.e. it adds H+). So, CO2's acidic properties cancels kalk's base properties. The left over component is HCO3- which is a bicarbonate...the same bicarbonate we add as a buffer in our 6 to 1 ratioed DIY buffer. This is the 6 part of the buffer...the bicarabonate part in Sodium Bicarbonate. The bicarbonate will eventually convert to carbonate since it may not be favourable (due to pH). The combination of bicarbonate and carbonate concentration is what forms our alk.
As you can see, you need some sort of CO2 for the kalk to add alk to your tank. Why does kalk cake on the surface of the kalk mix ? Well, that is what happens when there is too much CO2, but there isn't enough CO2 to convert the Calcium carbonate back to Ca++. So, it is sort of a funny boundary state.
- Victor.
|