For lowering or removing TDS, A4146 is a great resin to use. It comes in a blue & black resin (1:1 ratio) and when exhausted turns orange.
What is Purolite DI?
Purolite is a mixture of strongly acidic cation exchangers in in 1: 1 volumetric ratio of Purolite A4146 in hydrogen form and strongly basic anion exchange resin Purolite A4146 in hydroxide form.
Purolite A4146 has a specially designed indicator which by it's property of change of color from green to amber indicates its exhaustion.