TDS or Conductivity Monitor??? What should I buy?

[ronreef]

Which is the right one to use for detecting water quality out of an RO/DI system?

What are the right water quality ranges for the one you suggest?

I need to buy one soon. I don't know if my Spectrapure is putting out good product water.

Ron

[DgenR8]

I use this here:
http://www.aquaticreefsystems.com/TDS_Meters.htm
If you have an RO/DI, and it's properly maintained, even the dirtiest input water should have less than 5 PPM TDS once processed.