Originally Posted by Randy Holmes-Farley

CA-1 is a dye the binds calcium. It is a different color when bound to calcium and when not. The amount is not critical except to provide enough color. It is a weaker binder of calcium than the reagent in CA-3. Less of it may actually give a sharper endpoint, but may be harder to detect visually.

Ca-2 solution is a hydroxide solution to precipitate magnesium hydroxide and prevent it from being detected. The amount of it is not important as long as there is enough to precipitate the magnesium.

The titrant (CA-3) is a strong calcium binder (e.g., EDTA, but I'm not certain what exactly they use). As it is added, it binds up calcium. Eventually, the only calcium left that is not already bound to the CA-3 reagent is bound to the dye. At that point more added CA-3 strips away the calcium from the dye, and so the color changes as the dye transitions from calcium bound to free dye.

Originally Posted by Myka (Post 1023938)

Just an FYI for those of us who have done the tests enough times to not read the instructions anymore...

The Salifert Calcium test kits with an expiry 8/2022 now require 10 drops of Ca-2 rather than 8.

However, since both the Ca-1 and the Ca-2 are provided in excess, you shouldn't see much or any difference in the results.

Originally Posted by Frogger (Post 1023964)

Does this mean if we have old salifert test kits that we should be using 10 drops?

Originally Posted by FlamesFan (Post 1024141)

Myka would you mind linking the R2R thread with randy's comments?