i thought eriochrome black-T was a good indicator...ive used that for determining Calcium and magnesium ions present together in solution.
BUT, calcium titration is a special case.
Eriochrome black only forms a fairly weak calcium complex, and you often do
not get a good endpoint with calcium. One variant of the titration procedure is to use a back-titration. You add a measured excess of EDTA to the calcium-containing
solution, and then back-titrate by adding magnesium chloride solution until
you start to see the wine red colour from the magnesium complex. That means
that the measured amount of EDTA you added was used up in part by the
calcium ions originally present in the solution, and in part by the
measured amount of magnesium ions you added in the back titration.
i hope this explains it.