Meter Specs

Brad Gardner · #1 08/23/2002, 08:01 AM

I think I all ready know the answer but want to make sure. I am checking out a Conductivity and TDS meter (Combo). The Condutivity measures 0 to 3999 uS/cm and the TDS range is 0 to 2000 ppm. Can I measure salinity with this meter? I think salinity is 53 mS????

Thanks as always Randy!

Brad

Randy Holmes-Farley · #2 08/23/2002, 01:07 PM

You're right that the conductivity of natural seawater is about 53 mS/cm, or 53,000 uS/cm so that one won't work for tank salinity.

Brad Gardner · #3 08/23/2002, 01:10 PM

Thanks Randy. Then is that range for Conductivity good for anything in a reef tank?

Most of the meters I have looked at are that range (Hach. Lamonte, Hanna) except the VERY expense ones.

Randy Holmes-Farley · #4 08/23/2002, 02:28 PM

Yes, it is good for measuring the purity of fresh water (down in the few uS/cm range).

It is just a tad short of being suitable for measuring the saturation of limewater (about 9-10 mS/cm).

If you already have the meter and want to make use of it, you can dilute the tank water with RO/DI water by a factor of about 20 and then see what conductivity you have. We'd have to compare that to diluted seawater.

I don't have at hand the conductivity of seawater diluted that much, but we can do it as an experiment (though it will have to wait if I'm the one to do it as my conductivity probe resides at work

).

I do know that diluting seawater by a factor of 8 gives a reduction in the conductivity by a factor of about 6.7. So you cannot just do simple corrections. That's because the ions tend to be more free to move around when diluted.

FWIW, probes like the Pinpoint are not very expensive and do cover the range of interest (aroubnd 53 mS/cm). I agree that it is mostly the more expensive ones that cover both the 0-20 uS/cm range for freshwater and 53 mS/cm range for reef tank water.

Brad Gardner · #5 08/26/2002, 08:20 AM

Thanks Randy. I do have the Pinpoint Salinity Meter. Can I use it to measure TDS coming out of TAP and RO/DI unit?

Randy Holmes-Farley · #6 08/26/2002, 03:39 PM

I expect so. What is it's range?

Brad Gardner · #7 08/26/2002, 03:42 PM

0 to 60 mS. When people report their TDS, I think it is usally in ppm. I have a conversion to ppt. So getting ppm should be easy. Right?

Thanks,

Brad

Brad Gardner · #8 08/28/2002, 08:18 AM

Hi Randy,

When I used my Pinpoint Salinity meter to measure my water out of the tap = 1.3 mS, the RO/DI water from my LFS = 1.2 mS and my tank water = 53mS. Is there anything I can conclude about these readings?

Thanks,

Brad

Randy Holmes-Farley · #9 08/28/2002, 12:16 PM

Yes, that the meter probably doesn't read correctly below 2 mS/cm

Tap water is usually in the tens to hundreds of uS/cm, and RO/DI is usually in the single uS/cm.

Given that info, you can't likely use that meter on fresh water (but likely yes for the limewater). I think they have what they call a TDS or conductivity meter as well, and it is likely because the ranges don't overlap.

Brad Gardner · #10 08/28/2002, 12:44 PM

Thanks as always.

Yes Pinpoint does have a conductivity meter. It is around 120 and the accuracy is 1% of the display reading. The Hanna I am looking at has accuracy of 2% of Full Scale. Which one is more accurate or am I splitting hairs.

Thanks,

Brad

Randy Holmes-Farley · #11 08/28/2002, 12:54 PM

Hairs, I think, for what we typically want. Of course, if you are at the bottom end of 0-60 mS/cm and the error is +/- 2%, then the bottom might be 1 +/- 1 mS/cm.

If you are measuring tank water at 53 mS/cm, 1 or 2% accuracy is fine.