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TDS and refractometer calibration questions

mfisher2112

mfisher2112

Ok, so JRwholer (thanks JR!) put me on to a theory regarding my algae issue via a reefkeepers article he read regarding lack of calibration on a TDS meter that was giving false readings. So, I did some water checks, and got some rather quirky numbers.

I'm going to try recalibrating my TDS meter because there is NO WAY my straight tap water is 42ppm, and my water after a pur filter is 88ppm, so it's entirely likely my TDS is not 0 after RO/DI either. I have well water, and crappy well water at that. (and I'm embarassed to admit I have never recalibrated the TDS meter... dumb.dumb DUMB!)

So, 1st question, I'm looking at calibration solutions. I see it in 342ppm NaCL, and 1000ppm NaCL solutions. Which one?

2nd, what do you guys/gals use to recalibrate your refractometer? I figure since I'm calibrating, might as well do both of the tools I use the most!

I have found SEVERAL different calibration fluids for this. I did find one that calibrated to 53.0mS/1.0264SG/35ppt, but I've seen several that calibrate to 0 as well. Is it better to calibrate closer to the target or to calibrate to 0?
 
SirFragalot

SirFragalot

Matt, I recently purchased a handheld TDS meter that doubles as a thermometer and got simillar results. It turns out that I pushed the thermo button unknowingly and was reading those numbers instead. I'm not saying that is what happened to you, just putting it out there.
 
mfisher2112

mfisher2112

SirFragalot said:
Matt, I recently purchased a handheld TDS meter that doubles as a thermometer and got simillar results. It turns out that I pushed the thermo button unknowingly and was reading those numbers instead. I'm not saying that is what happened to you, just putting it out there.
Click to expand...

Thanks for the info tip. Definitely not hitting the thermo button, though.
 
M

mnat

Officer Emeritus
Staff member
Moderator
We calibrate our refractometer with fresh RO water (zero reading). I don't think is really matters what number you are calibrating to, as long as you know that number. Even the LFS I bought it at calibrated it in front of us with fresh water. It is always nice to save a bit of money in this hobby.
 
V

vangvace

mfisher2112 said:
Ok, so JRwholer (thanks JR!) put me on to a theory regarding my algae issue via a reefkeepers article he read regarding lack of calibration on a TDS meter that was giving false readings. So, I did some water checks, and got some rather quirky numbers.

I'm going to try recalibrating my TDS meter because there is NO WAY my straight tap water is 42ppm, and my water after a pur filter is 88ppm, so it's entirely likely my TDS is not 0 after RO/DI either. I have well water, and crappy well water at that. (and I'm embarassed to admit I have never recalibrated the TDS meter... dumb.dumb DUMB!)

So, 1st question, I'm looking at calibration solutions. I see it in 342ppm NaCL, and 1000ppm NaCL solutions. Which one?

2nd, what do you guys/gals use to recalibrate your refractometer? I figure since I'm calibrating, might as well do both of the tools I use the most!

I have found SEVERAL different calibration fluids for this. I did find one that calibrated to 53.0mS/1.0264SG/35ppt, but I've seen several that calibrate to 0 as well. Is it better to calibrate closer to the target or to calibrate to 0?
Click to expand...

Your best bet is to find the manual for what ppm solution your TDS meter calls for. If you bought it though AWI they should be able to tell you as well. Calibrating the meters is why I still have a handheld meter instead of a inline one.

What reference point you calibrate your refractometer to is of great debate on many a forum in the hobby. I personally prefer to calibrate it to what I'm actually going to use it for. That way I relegate the possibility of a slope error in my meter. If I calibrate it to 35ppt and it comes out to 0 when I use RO water then I won't use a cal solution again until I bang the meter into something. Not that the happens... :-[

Refractometers and Salinity Measurement - RHF
 
mfisher2112

mfisher2112

vangvace said:
Your best bet is to find the manual for what ppm solution your TDS meter calls for. If you bought it though AWI they should be able to tell you as well. Calibrating the meters is why I still have a handheld meter instead of a inline one.
Click to expand...
Thanks! Mine is a handheld from air water ice that came with the typhoon III. Just looked it up and their meters are apparently factory calibrated to 342 NaCL solution. That's what I was looking for, so that's what I will go with then.


What reference point you calibrate your refractometer to is of great debate on many a forum in the hobby. I personally prefer to calibrate it to what I'm actually going to use it for. That way I relegate the possibility of a slope error in my meter. If I calibrate it to 35ppt and it comes out to 0 when I use RO water then I won't use a cal solution again until I bang the meter into something. Not that the happens... :-[
Click to expand...

I think that's about what I was reading doing some research. Calibrate to your target to avoid the potential slope. Apparently the further away from your calibration point you get, the less accurate the meter becomes. Which makes sense to me, so I think that's the way I will go with it.

And yeah, mine has never been banged before! ::) (imagine that! LOL!)
 
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