TDS meter opens my eyes

[James983]

So I finally breakdown and spend the $20 on a HM Digital TDS meter. I immediately test my tank water, 10 PPM with RO/DI water. Not a great reading, so I change all filters and flush the RO membrane. Reading from RO/DI then, 006 PPM. I guess 0 PPM is not possible with these little RO/DI filters. Anyone have 0 PPM from a home unit? By the way mine is a Coralife 50gpd with a spectra pure DI.

Then I check my mixed saltwater in my Rubbermaid trash can. All I keep getting is a ERR reading. This reading is not addressed in the paperwork that came with the meter. My fear is that the TDS is too high to read. So I discarded 15 gals of new saltwater that was prepared for a water change. My question is, what does everyone use for their water change water?

[bjromaine]

I have a PurelyH2O RO/DI unit with a dual in line TDS meter.
I get 0ppm from the output......

I have never measured the tank water.....

Not familiar with your meter but does it require pressure (water moving) to get a reading? If so, that might be your problem

[Bojan]

[i]Then I check my mixed saltwater in my Rubbermaid trash can. All I keep getting is a ERR reading. This reading is not addressed in the paperwork that came with the meter. My fear is that the TDS is too high to read.

You are right. Reading is too high.

TDS meter is acctually conductivity meter. TDS meter in salt water can be used to measure salinity, but most od TDS meter can not measure so high conductivity.

Conductivity of the NSW is 35 mS/cm

Measuring range of the typical TDS meter is 9,9 mS/cm.

[KAiNE]

add another DI chamber, you will see 0 TDS.

[AZDesertRat]

Normal saltwater is above the range of the TDS meter, don't try it or it can possibly ruin your meter. Make sure you rinse it well after that first attempt. I am assuming you have a handheld meter?
0 TDS is easily possible with a good RO/DI system. You need to do a few tests to see if your unit is functioning as it should. First get a squeaky clean glass drinking water glass with no deposits or water spots of any kind nor soap residue. Let the RO/DI unit run for several minutes then fill the glass and test your tap water TDS, record the reading, triple rinse the glass and meter in DI water, do the same with RO only (without DI) and again triple rinse both the glass and meter. Finally test the finished RO/DI and do a final triple rinse. Always put the glass and the meter away squeaky clean for next time.
What is your tap water TDS? What is your RO only TDS? Is the RO only somewhere around 96 to 98% less than the tap TDS? If not you may be in need of a ned RO membrane. If your RO is functioning as it should the DI should be 0. You should not need a second DI chamber, with my previous unit I could get about 150 gallons of 0 TDS water with a tap water TDS that exceeds 800 so it is entirely possible.

[James983]

OK, I'm gonna add another DI chamber. Is a rubbermaid container good for mixing salt?

[AZDesertRat]

Do the tests I described before wasting money on a second DI, I do not think you will need it.

[James983]

Az didn't see your post before my last one. Gonna do the test you explained.

[James983]

Well Az, I just performed the tests you explained. TDS of tap water was 47 PPM, TDS after RO was 001 PPM, TDS after DI was 0 PPM. Aparently the variable was the squeky clean glass. I made sure it was washed with RO/DI water and bone dry for each test. Thanks to all for your help.

[AZDesertRat]

If you are using high quality prefilters and carbon blocks, your membrane is in good condition, your tap water TDS is not something way out of sight, your new DI resin was fresh and stored properly (kept sealed and moist) and you are using the unit enough to keep the filters wet and well flushed then you can get 0 TDS with the combination you have. I don't know what RO membrane Coralife uses but if its a 50 GPD is should be in the 96 to 98% rejection range when new and should remain close to that for several years providing you have kept up with the regular maintenance (ie changes and disinfection at 6 mo. intervals), used good filters to protect it and kept the waste ratio in the 3 or 4:1 range.

[AZDesertRat]

Thats good! With a tap TDS of only 47 and an RO of 1 or 2 you should easily get over 1000 gallons out of a 24 oz DI refill.
I requisitioned a good glass from the Wifes kitchen and use the same one every time. After cleaning it I turn it upside down for storage so dust and whatever does not get in it between uses.