Who is correct: Water hardness test

[smallpooldad]

Some persons state that when crystals start to form this is when the measure should be taken others when it starts to turn blue. Difference is 250 for first and 375 for second. The pool does have metals in solution so I normally add three drops of the last component to bind them adding this to the overall measure; Taylor kit is used.

So who is correct?

[waterbear]

The cryatals are precipitated magnesium hydroxide and possibly other metals that might be in the test sample. The first reagent in this test is sodium hydroxide to raise the pH and precipitate out the magnesium so you can get a reading on the calcium hardness alone. the endpoint is when the calcon indicator changes to blue (not violet). Best way to find the endpoint is to add the titirant until no further color change is noted and not count the drop that didn't produce any color change. If there are metals present try adding 6 drops of the EDTA titrant first. You might find the color change easier to see.