TDS Question/Help

[rgunn1]

Ok, so I bought a handheld TDS meter off of ebay. I do not currently have an RODI unit, so I buy all my RODI water from the LFS. I will be getting an RODI unit soon so I went ahead and bought the meter. Plus I was curious as to what the TDS readings were on the water I buy.

I used the meter on my tap water and got a reading of 32, which seamed reasonable for tap water. Then I used it in my display tank and got an error (I later realized this meter is only for freshwater). So I used it in my 10 gallon tank that I used for top off water and got a reading of 419!!! This cant be right, right? I still had about a gallon of the same exact water in a 5 gallon plastic container. I tested that and got a 106?!?! It's the same exact water! Does the storage of RODI water change the TDS reading? Could this water have been a 0 TDS (like the LFS claims) and then 3 days later be a 419 after sitting in a 10 gallon tank, and 106 after sitting in a plastic container? What am i missing here? FWIW, my Nitrates and Phosphates are virtually 0 in my display tank and all corals and fish are healthy and happy.

 

[rdnelson]

When you tested the salt water you were reading the salt,calcium, magnesium, etc that is mixed into the 0 TDS. Those things are "Disolved Solids" so it very well could be that high. Next you checked the top off. I suspect there was still salt water residue on the hand held. The reason it was lower was because you diluted it when you put it in RO. The next time you put it in RO it was lower because you diluted it further.

Rinse it well with RO and I bet it keeps coming down.


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[sewer urchin]

You may want to check the owner's manual about calibrating the unit. I'm only guessing here, I think that the saltwater error reading may have knocked the unit out of range. Also Rich's idea sounds very plausible as well... calibrating should solve both issues. I don't know if all units have the ability too be calibrated or if it's a function of the more expensive ones

 

[rdnelson]

Sewer Urchin;854940 wrote: You may want to check the owner's manual about calibrating the unit. I'm only guessing here, I think that the saltwater error reading may have knocked the unit out of range. Also Rich's idea sounds very plausible as well... calibrating should solve both issues. I don't know if all units have the ability too be calibrated or if it's a function of the more expensive ones

I agree completely but.... Make sure all residue is off before you calibrate. Otherwise you could be mid-calibrating it.


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[rgunn1]

That all makes sense, thanks for the help!!