RO/DI troubleshooting help

[MrSandman]

I've got a 4 stage RO/DI filter with a DM1 inline TDS monitor.

Incoming tapwater is 340ppm
DI output is 9ppm
RO output is 16ppm

So based on my calculations the RO is rejecting about 95%. I don't have the specs. on the RO membrane but i believe this should be fine.

So i replaced the filter block and carbon block and the DI block and the DI output dropped down to 2 PPM.

So my question is.....what is the problem? Why can't i get it down to 0?

I have an 800 PPM calibration solution and based on the temp/ppm chart on the solution the TDS monitor appears to be reading just fine.

I'm baffled. Any ideas?

[Kenmx10]

Do you have at least 65 water pressure. If not it could be dropping by the time it reaches your last filter. . That could cause your tds to read higher.

[MrSandman]

Originally posted by Kenmx10
Do you have at least 65 water pressure. If not it could be dropping by the time it reaches your last filter. . That could cause your tds to read higher.

My water pressure reads fine. My TDS isn't going up. I just listed them out of order in my initial post.

I think i found my problem. I tried switching the probes on my TDS monitor and put the input probe on the output line and it reads zero now. Looks like the output probe may be bad. Unfortunately the TDS monitor probes can't be adjusted individually so its most likely toast. I'll be buying the DM2 model where the probes can be adjusted individually. Lesson learned.