|the water before treatment|
If you are really worried about calcium deposition, you can use the Langelier Index. This says that deposition occurs at a pH equal to the equation A+B-C-D, the constants are in the link above. A is a constant for temperature (around 2), B depends on total dissolved solids (TDS is 0 in rainwater, so B=9.7), C and D are also the minimum of 1 for rainwater. That gives me an answer of pH 10. So as long as we keep the water below pH 10 we won't have calcium deposition. This did make me realise that we need to be able to remove the limestone when the pH is just above 7, so it doesn't keep creeping up.
It took me a little while to find limestone. Eventually I went to the local landscape supplies centre and asked for a few scoops of "white rock" which I was pretty sure was limstone. To check if I bought the right rock, first I sprayed a rock with vinegar, and it bubbled, probably limestone. Then I put a bag of the stones in a bucket of our water and tested the pH before and after 24 hours. The pH changed from 4.9 to 9.7. So I was pretty convinced that I had limestone. You can use these tests to check if you can't be sure what you're buying.
|"white rock" from landscape supplies|
|the rock fizzed when I sprayed it with vinegar|
|The water pH increased quickly after I added some limestone|
Do you collect rainwater? Ever thought to test the pH?