I can answer this question. I have kept saltwater/reef aquariams for close to 30 years now and the calcium hardness test is a standard one for saltwater so I am familiar with the chemistry involved. If there are other metals present (copper is a main problem but other metals can affect it) your endpoint will turn purplish and not a distinct change to blue. You might even notice what seems like purple particles suspended in the liquid. The anser is to add about 5 or 6 drops of the EDTA (reagent #3 in Ben's or Taylor's kits) FIRST before you put reagent #1 in your test sample. This will bind up the metals. When your do your titration count those drops! (for example, you add 5 drops first and then your titration takes another 15 drops = 20 drops total which is 200 ppm calcium hardness)


Wow! Can anyone else verify this??? If so, we should include it as part of the CH test!

I AM impressed!