TDS meter calibration

masonicman · 09/04/2008, 10:26 AM

What can I use if any, besides the manufacture's solution to calibrate my TDS meter?

Randy Holmes-Farley · 09/04/2008, 11:14 AM

I generally do not believe that TDS meter calibration is necessary or useful when used to monitor RO/DI. There are, in fact, several different ppm TDS unit scales, and few reefers actually distinguish them anyway.

The thing that gets off in a TDS meter is not the zero point, but just the slope, so if 100 ppm TDS really reads as 110 ppm TDS, then at 1 ppm TDS, the reading will be 1.1 ppm TDS (which rounds to 1 ppm TDS).

With that being the case, there are two things that you use TDS for:

1. Monitoring RO performance by the ratio of TDS in to TDS out. That ratio will be unchanged by calibration.

2. Monitoring when a DI is depleted. Since I recommend replacing the DI as soon as you detect a rise in TDS, it does not matter exactly whether the TDS is 1.0 ppm or 1.1 ppm or 2 ppm or whatever when you detect it: it is time to replace the DI when it goes above 0 ppm.

That said, there are a few spring water brands that put TDS readings on the label that may allow inexpensive calibration if you want to do so, but do not want to buy a commercial standard. So you might check in the grocery store next time you are there.

crvz · 09/04/2008, 11:40 AM

Well Randy used a lot more words than I planned to, but I don't ever calibrate my TDS meter, for the reasons he explains.

masonicman · 09/05/2008, 05:50 AM

Thanks Randy. I wanted to email you this question directly but your email is blocked.

Randy Holmes-Farley · 09/05/2008, 10:14 AM

You're welcome.

Better to ask/answer it where others can see it anyway.

Happy reefing.

09/04/2008, 10:26 AM	#1
masonicman Registered Member Join Date: Aug 2007 Location: NJ Posts: 1,313	TDS meter calibration What can I use if any, besides the manufacture's solution to calibrate my TDS meter? __________________ It is better to ask for forgiveness then to ask for permission.......... Current Tank Info: 75 gal mixed reef, 216w LED, Remora Pro skimmer, HOB fuge, 400w htr, ATO RO/DI, 90lbs LR and 1" SB.

09/04/2008, 11:14 AM	#2
Randy Holmes-Farley Reef Chemist Join Date: Apr 2001 Location: Arlington, Massachusetts Posts: 86,233	I generally do not believe that TDS meter calibration is necessary or useful when used to monitor RO/DI. There are, in fact, several different ppm TDS unit scales, and few reefers actually distinguish them anyway. The thing that gets off in a TDS meter is not the zero point, but just the slope, so if 100 ppm TDS really reads as 110 ppm TDS, then at 1 ppm TDS, the reading will be 1.1 ppm TDS (which rounds to 1 ppm TDS). With that being the case, there are two things that you use TDS for: 1. Monitoring RO performance by the ratio of TDS in to TDS out. That ratio will be unchanged by calibration. 2. Monitoring when a DI is depleted. Since I recommend replacing the DI as soon as you detect a rise in TDS, it does not matter exactly whether the TDS is 1.0 ppm or 1.1 ppm or 2 ppm or whatever when you detect it: it is time to replace the DI when it goes above 0 ppm. That said, there are a few spring water brands that put TDS readings on the label that may allow inexpensive calibration if you want to do so, but do not want to buy a commercial standard. So you might check in the grocery store next time you are there. __________________ Randy Holmes-Farley Current Tank Info: 120 mixed reef

09/04/2008, 11:40 AM	#3
crvz Team RC Member Join Date: Jul 2005 Location: houstonia Posts: 7,989	Well Randy used a lot more words than I planned to, but I don't ever calibrate my TDS meter, for the reasons he explains. __________________ -Chris- You don't win friends with salad. "Look! They're trying to learn for free!" ... "Use your phony guns as clubs!" Current Tank Info: rectangluar? wet?

09/05/2008, 05:50 AM	#4
masonicman Registered Member Join Date: Aug 2007 Location: NJ Posts: 1,313	Thanks Randy. I wanted to email you this question directly but your email is blocked. __________________ It is better to ask for forgiveness then to ask for permission.......... Current Tank Info: 75 gal mixed reef, 216w LED, Remora Pro skimmer, HOB fuge, 400w htr, ATO RO/DI, 90lbs LR and 1" SB.

09/05/2008, 10:14 AM	#5
Randy Holmes-Farley Reef Chemist Join Date: Apr 2001 Location: Arlington, Massachusetts Posts: 86,233	You're welcome. Better to ask/answer it where others can see it anyway. Happy reefing. __________________ Randy Holmes-Farley Current Tank Info: 120 mixed reef