Output of RO at 0 TDS?

[konkers]

I recently bought the deluxe RO/DI system from BRS which came with a dual TRS meter hooked up to the input and out put of the DI stage. When I first installed it the input TDS read ~5ppm. Within a few days it started reading 0ppm. Is this possible? The same meter hooked up to tap water reads 27ppm.

[Randy Holmes-Farley]

With the tap that low, yes it is possible that the RO effluent, which is typically 0.02 to 0.1 times the TDS of the tap water) is low enough that the meter rounds to 0. Mine runs about 0.05 times the TDS of the tap water, and if that was true for yours, it would be 0.05 x 27 = 1.3. Your membrane may be better, or the meter may not be especially accurate at that low level. :)

Your DI will last a long time. :)