Hardness, Total Hardness, Carbonate Hardness, TDS, and so on

[chita]

There's actually little difference between meters with regard to the conversion factors from EC to TDS, purely a manufacture thing, determined as much by the choice of components as other factors.

However if like me you decide to utilise both EC and TDS meters, be sure they are either from the same manufacturer or first establish that the applied conversion factors are the same. Otherwise the two readings will not correspond in any meaningful way!

I find that the TDS meter usually responds to small changes a little quicker than the EC meter, but there's actually no real need to have both.

Personally TDS and ORP would be my two first choices for meters.

Chi