chem geek.. thats just what I was looking for, thanks.
In the last three months I have added 116 tea spoons of 55% Chlorine granules. That equates to 548 g. The calculator shows that my CYA will be at 163. Taking into account a loss of 5 ppm per month, then it will be around 148. I think I am right in saying that anything over 100 is too high, so although the water looks fine I will be changing it today after 101 days.
I have been shocking with MPS, but I have recently done a dichlor shock so that has added to the CYA in recent weeks.
(just by using your estimate of 1 teaspoon of dichor adds 1.4 ppm of CYA also equates to 162.4 ppm (116x1.4) so that is a good guide for me)