TDS reading -does it make sense?

[yraveh]

I have installed a nes maxicap RODI 90gpd.
(http://www.spectrapure.com/manuals/MAXCAP_RODI_MANUAL.pdf)

After 2 hours runnning the inflow to RO reads 140ppm;out 2ppm.
The inflow to the DI carrtridge that is more downstraem reads 17ppm and outflow of 12 ppm.

Q1: How could the DTS reading increase from 2 to 17 when passing through the first DI resin? it makes no sense to me.
Q2:is 140 ppm high relative to other cities?
Q3: is 12 ppm not to high or can I use it?

Thanks

[Randy Holmes-Farley]

I have the same system. My meters, in order, read 100 ppm, 2-5 ppm, 0 ppm, 0 ppm.

As I understand it, the TDS meters read tap, RO effluent, post DI#1, Post DI#2.


What are all four of your readings in order of flow?

FWIW, the TDS coming out of a DI can be higher than going in if the DI has been depleted.

140 ppm TDS is mid to low for tap TDS.

The effluent from the final DI should read 0 ppm. I would replace the second DI if it reads higher. Maybe swap it to the first position,a nd put a new one in the second (downstream) position.

[yraveh]

Randy,
Indeed the TDS meters read tap (i.e. post sediment&carbon filters), RO effluent, post DI#1, Post DI#2.

Each TDS metergives 2 measurement:

Meter 1 (left)
Pre RO -140
Post RO- 2

Meter 2( right)
pre DI resin second cartridge - 17
Post (=effluent) 12

Why would a brand new cartridge be depleted?
I bet a faulty meter is more likely. I will try to swap them and see the readings.

BTW in your article RODI you did not discuss the waste to product ratio (of 4-6). Is that a major issue?
Thanks

[Randy Holmes-Farley]

Could either be a faulty meter, or shot DI resins.

I'm not sure on the waste question. The exact ratio is fairly unimportant for output quality,although it may be important for water conservation if that is important in your area.

[David Grigor]

In Twin Cites MN, tap is 230-250ppm. High in nitrates from all the water runoff to area lakes.

So compared to here 140ppm tap is good ......