Testing water for CPs with refractometer

[Brokken]

Has anyone tried using a portable refractometer like the ones sold to test the SG of salt water to determine the quality of the water for CPs?

 

[Clue]

You could always use a TDS meter intended for freshwater aquariums.

 

[Brokken]

I'm only asking because I already have a refractometer from my salt-water reef days.

 

[theyellowdart]

I don't really understand how it would work. Refractometers only measure the amount of dissolved salt.

What about a freshwater test kit? That could do the trick.