Erio T, or Eriochrome Black T, is a complexometric indicator used to quantify magnesium and calcium ions. In a water sample, the sum of calcium and magnesium ions is known as total hardness.
In its deprotonated form, Eriochrome Black T is blue. It turns red when it forms a complex with metal ions.
We sell Eriochrome Black T as a 1% powder with sodium chloride in 5g bottles.