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RE:CaOH and KH

I don't think CaOH will work for increasing your KH. You want to 
increase the concentration of CO3(-) in your tank. That is why adding 
Na2CO3, or CaCO3 or KCO3 works. This adds to the buffer. I don't know 
how much chemistry you know, but basically you have a mix of CO2 
which you can think of as an acid and the CO3- which you can think of 
as a Base. Acids lower pH and Bases raise it. So the CO2 will react 
with the bases you add and the CO3 will react and decrease the change 
in pH when acids are added. Now the CaOH is a weak base but if your 
CO2/CO3 buffer is dilute( low KH and little CO2) you would get an 
increase of your pH into the high numbers. If you want to add Ca and 
you have soft water and want to increase the KH( a measure of 
carbonate ions) I would add CaCO3, calcium Carbonate.

Also KH is the measurement of Carbonate Ions, while GH is a measure 
of Sulfate ions, mostly Calcium sulfate and Magnesium sulfate. I just 
looked at your question again and I see you wanted to increase the Ca 
concentration, well I think CaOH will do that. However be ready for 
your pH to increase. You may need to add more baking soda and CO2 to 
make your buffer stronger and keep your pH in the acid to neutral 
range, that I am assuming it is in now.

I hope this helps, feel free to ask for clarification.

Larry Jones
Medical student.

PS the CO2/CO3 Buffer is a major component used to keep human blood 
at pH 7.35 :)