TDS Meter Reading?

[The Saltwater Kid]

I just bought a TDS meter and tested my R/O DI water and got a 024 reading...is that good or bad? The water was in a bucket that I filled last night so it has been sitting around all day today, would that make a difference? Also, I think it's time to flush my TFC membrane in my R/O DI unit as it's recommended by the manufacturer to do so once per month. Thanks!

[indydog1]

i believe that the reading should be zero. it may be time to flush or replace the membrane. but it isnt that bad.

[AZDesertRat]

Never test from a bucket or storage vessel, you will get inaccurate readings due to contaminates in the plastic, salt or other residue from water changes, CO2 etc.
I use a squeaky clean clear drinking water glass with no water spots or soap residue for accurate tests. Always fill it directly from the unit.
0 TDS is the goal from RO/DI. My method of testing goes like this.
1. Get a sample of the tap water, insert the probe and let it stabilize. Record the reading and triple rinse the meter probe and the glass in DI water.
2. Get a sample of the RO only before DI, again let the temperature and reading stabilize, record the reading and do the triple rinse with DI again.
3. Finally get a sample of the final RO/DI water and as above do a final triple rinse with DI and you are clean and ready for next time. I dry the glass and turn it upside down to keep dust and salt out of it and cap the meter tightly.

You should be seeing a 96-98% reduction in TDS with the RO only. Say your tap water TDS is 200 then you can expect a RO reading of 4 to 8 TDS or so. The lower the better. The RO/DI should be 0 or very close to it. Once you start to see anything other than a consistent 0 its time to change the DI cartridge as it is becoming exhausted and starting to release weakly ionized substances like phosphates and silicates into the treated water.

Flushing a membrane once a month does nothing. Membranes are constantly flushed with the 4:1 water ratio provided by the flow restrictor. Flush valves have no proven value. In order to be the least bit effective they would have to be used each and every time you shut the RO unit off to flush any accumulated solids away from the membrane. Once they are allowed to stay they begin to solidify on the membrane and no amout of flushing will helpo at that point. Just keep you waste ratio at 4:1 and you are doing the most good.

[RetroAndreas]

My TDS with a RO store called Water Depot is always 1ppm.

I think under 5ppm is acceptable using a RO filter system and with DI 0ppm should be expected

[The Saltwater Kid]

My DI cartridge is only showing a small ring of orange on the bottom so it shouldn't be exhausted! I will check the next time I need water and add some directly from the unit to a clean glass and see what it reads then.

[The Saltwater Kid]

I just measured my tap water and got a 147 reading.

[The Saltwater Kid]

bump

[AZDesertRat]

Color changing resin is very unreliable, do not depend on it for accuracy.
Get the three TDS readings I suggested, tap, RO only and RO/DI, you need all three to troubleshoot your system.