Conductivity 101 please.....

kidney514

kidney514

Premium Member
Hi!

Just acquire a conductivity probe for my Profilux device and have some question about conductivity.

1st What is the proper way/unit of measure to check salinity.
mS
PSU
kg/l
or they are all good.

2nd what is the target that one person what to achieve.
so far I was alway keeping it @ 1.025 +-.001

But now I am confused here is why

Hydro: 1.0268
Refrac: 1.0265

New toys/conductivity probe: 1.0213 or PSU 32.11 or 49.4 mS @ 80.9F

I am assuming that the Probe that I just got and is freshly calibrated in a solution of 50mS is the one that is correct?

Shoud someone base everything on that conductivity probe and raise salinity?

PS I have read this, but the mistery remains: http://www.aquariumfish.com/aquariumfish/detail.aspx?aid=1804
 
Don't assume anything ... it will only get you in trouble ... I assumed Boomer liked me ;)

Here is one from the boomer archives (I think) ...
http://www2.dpi.qld.gov.au/horticulture/3096.html

PINPOINTâ"žÂ¢ Salinity Monitor
Conversion Chart

mS | ppt | SG
51.0 33.50 1.0248
51.5 33.90 1.0250
52.0 34.30 1.0253
52.5 34.60 1.0256
53.0 35.00 1.0259
53.5 35.40 1.0262
54.0 35.70 1.0265
54.5 36.10 1.0268
55.0 36.50 1.0270
55.5 36.80 1.0273
56.0 37.20 1.0276
56.5 37.60 1.0279
57.0 38.00 1.0282
57.5 38.30 1.0285
58.0 38.70 1.0288
58.5 39.10 1.0291
59.0 39.50 1.0294
59.5 39.80 1.0296
60.0 40.20 1.0300

Hope this helps ( I took the chart from another thread)
 
First, that PinPoint table is off. NSW @ 25 C , 35 ppt (PSU) = 53,065 uS or 53 mS .

This is just out. Use the "Resulting Salinity Calculator"

Enter zero for the water change amount to use this as a salinity conversion calculator.


http://www.hamzasreef.com/Contents/Calculators/


Something is wrong /say, see below. If it was not ATC it would numbers higher, like 53mS if the temp was 81 F.



CT = C25 [1 + 0.021 (T - 25)]
CT = measured conductivity of a solution at sample temperature
C25 = the conductivity of the solution at 25C ( 77F) and T = the sample temperature (C)

In your case if we assume it is not ATC.

Then
CT = 50 mS[1+0.021( 2.16 )] = 52.27

If it is ATC

Then
CT = 50 mS[1+0.021( 0 )] = 50

So it appears you just need to get a 53 mS solution and it is ATC

CT = 53 mS[1+0.021( 0 )] = 53 = 1.0264 = 35 ppt

I am assuming that the Probe that I just got and is freshly calibrated in a solution of 50mS is the one that is correct?

As Jansen pointed out, DO NOT assume. Get some PinPoint 53 mS solution and recal it. When you say "assume" are you saying it came that way or YOU recalibrated it to 50 mS. And at what temp did you cal it at. It is best to do it @ 25 C (77F)

For now I would stay with the refract and or hydrometer. The 3 are ~ equal, it is just that 50 mS
 
<a href=showthread.php?s=&postid=12833848#post12833848 target=_blank>Originally posted</a> by Boomer
First, that PinPoint table is off. NSW @ 25 C , 35 ppt (PSU) = 53,065 uS or 53 mS .

This is just out. Use the "Resulting Salinity Calculator"

Enter zero for the water change amount to use this as a salinity conversion calculator.


http://www.hamzasreef.com/Contents/Calculators/


Something is wrong /say, see below. If it was not ATC it would numbers higher, like 53mS if the temp was 81 F.



CT = C25 [1 + 0.021 (T - 25)]
CT = measured conductivity of a solution at sample temperature
C25 = the conductivity of the solution at 25C ( 77F) and T = the sample temperature (C)

In your case if we assume it is not ATC.

Then
CT = 50 mS[1+0.021( 2.16 )] = 52.27

If it is ATC

Then
CT = 50 mS[1+0.021( 0 )] = 50

So it appears you just need to get a 53 mS solution and it is ATC

CT = 53 mS[1+0.021( 0 )] = 53 = 1.0264 = 35 ppt

I am assuming that the Probe that I just got and is freshly calibrated in a solution of 50mS is the one that is correct?

As Jansen pointed out, DO NOT assume. Get some PinPoint 53 mS solution and recal it. When you say "assume" are you saying it came that way or YOU recalibrated it to 50 mS. And at what temp did you cal it at. It is best to do it @ 25 C (77F)

For now I would stay with the refract and or hydrometer. The 3 are ~ equal, it is just that 50 mS
Click to expand...
Well I guess it's a good thing I don't use Pinpoint!! I use GHL Profilux a top notch controller that has never failed me so far. But the huge gap between the Hydro/refrac and the Salinity probe scares me, but the past has show that profilux has been right!
If you look @ my first post does my profilux look right (boomer)?
 
Yes I looked at your first post and no it does not look right and why the long post I gave.


New toys/conductivity probe: 1.0213 or PSU 32.11 or 49.4 mS @ 80.9F

Should be 1.0213 = 28.295 PSU = 43.886 mS. So, your numbers make no sense at all :)


When I said PinPoint, I meant the PinPoint 53 /mS calibration solution, which is right on. It is just their table that is off. And the only part that is offf is the SG as it is for a 20 C hydrometer and not a 25 C hydrometer, which we use. And the sample water is 72 F, which is nonsense. You should not be using 50 mS, it will be off some.

I use GHL Profilux a top notch controller

I will have to dispute that :) It is not top notch in the "real world" of controllers ;) It is a very nice unit for home aquariums.

but the past has show that profilux has been right!

Based on what it is right on ? Even with a 50 mS solution you should not be that far off as you are. So it is the meter or both the refract and the hydrometer. I don't buy both being wrong and the meter right.

You did not answer the questions

1. Who's hydrometer and what kind

2. Who's refract and how was it calibrated

No matter how I look at either of these it is still the meter/probe.
 
<a href=showthread.php?s=&postid=12838153#post12838153 target=_blank>Originally posted</a> by Boomer
1. Who's hydrometer and what kind
Click to expand...

Instant Ocean Float

2. Who's refract and how was it calibrated
Click to expand...

GEneric and have checked with RO/DI

No matter how I look at either of these it is still the meter/probe.
Click to expand...
I guess I could tweek the cal to match the other device,
 
No, you don't DO that :) A bottle of Pinpoint 53 mS is like $ 3.45 USA. This stuff can also be used to cal your refract and check you IO. It is one cal. solution for all 3 :)

Lets look at those refract and Sg numbers now.

If a refract is calibrated in RO/DI and it is lab grade it will read 1.5 ppt to low

1.0265- ~.0015 = 1.0221 and you meter reads 1.0213. But cheap refracts can be of more than that 0.0015. So we could say the meter is right on

A swing arm hydrometer may read to high if it has bubbles on it. So, it would be below 1.0268 and could be = to your cond. meter, if it had no bubbles. If it has never been cleaned it will read to low so the Sg will really be higher, which can not conform to your cond meter at all or refract.

New toys/conductivity probe: 1.0213 or PSU 32.11 or 49.4 mS @ 80.9F

As I said these numbers are way off.


Go here and type "hydrometer reading" 1.0213 and "sample temp" 80.9 = 29.92 ppt/PSU

http://www.reefkeeping.com/issues/2004-07/rhf/conversion.htm


If you take that Salinity 49.4mS and go here.

http://www.ultrasw.com/alcock/creeks/sal.shtml

and type in 49,400 @ 27.166 C = 30 .8 ppt and you get 32.11 ppt/PSU on your meter.

So on these notes also I see a probe/meter issue. Just a thought, at times these meters get RF interference so try to shut off all power near the meter, i.e., lights , pumps, ect.. and see if the readings change.
 
We had a similar discussion in the past in another thread here.

There are several conversion charts for conductivity<->salinity<->density
and all are different!

We created an "average" table, combined this with our experience, made research and found formulars for converting. Of course we take in account the temperature during calibration and the actual tank temperature.
These calucations are based on the so-called "Kopenhagen water", this has a special mixture of salts.
Since not all salt mixtures in the tanks are the same the conversion from conductivity to density or salinity is not always 100% correct.
This is not because Profilux is "not a nice a controller for home aquariums" (in fact ProfiLux runs in several institutes, e.g. Leibniz-Institute Kiel, Aquarium Plymouth, Alfred-Wegener Institute for polar research, ...), the reason is that only conductivity is measured, the other values are calculated based on an assumed salt combination.

But: In the next firmware we will offer the option to "calibrate" the salinity by adding an offset - so everyone can adjust the readings for his water.

Calibration: As mentioned the calibration is temperature compensated. But to eliminate slight measurement errors and to obtain best results we recommend to calibrate at exact 25°C
 
Im a lil confusedhere Matt. Are you saying that boomers way of gettingspecific gravity is wrong ? (1.0213 = 28.295 PSU = 43.886 mS)
 
These calculations are based on the so-called "Kopenhagen water", this has a special mixture of salts

This is 100 % true

Since not all salt mixtures in the tanks are the same the conversion from conductivity to density or salinity is not always 100% correct.

This is 100 % true also. It does not need to be 100 % correct. Your meter is not 100 % correct no meter is ;)

We created an "average" table, combined this with our experience, made research and found formulas for converting. Of course we take in account the temperature during calibration and the actual tank temperature.

Not the way to be scientific at all ;)


One could take either a refract, hydrometer or a conductivity meter and get a NSW level using just table salt. However, Matthias you guys are way off in your assumption. Table salt, NaCl, being taken to a NSW level, 53, 065 uS, an Sg of 1.0265 on any of these " meters" and I will assume you would agree that is more than substantially off from NSW/Kopenhagen , is off only ~ 1.5 ppt. And ASW is not going to be off any where near that amount from ASW brand x, y, or z, when compared to NSW If you take a conductivity meter and calibrate it properly, a refract and calibrate it properly and use a certified hydrometer and correct for temp the difference between salts is very little difference and is even well with in the margin of accuracy of the "meter'. So the comment you made and are trying to "defend" yourself with is meaningless.


If your claim that this is correct you are off

1.0213 or PSU 32.11 or 49.4 mS

49,400 = 31.2

There are several conversion charts for conductivity<->salinity<->density
and all are different!

Where show me, I use std NSW ones and they are all the same or almost the same and the off-set is meaningless.

I will add and maybe you don't know this but DENSITY does NOT = Specific Gravity. The Density of NSW @ 25 = 1.0234 and its Sg = 1.0264 (corrected). You don't correct for Density, just Sg. Denstiy is density but Sg is not always Sg , as there are different calibration point Sg hydrometers.

http://www.phys.ocean.dal.ca/~kelley/seawater/density.html

When using a std seawater hydrometer @ 15 C that Density of 1.0234 becomes an Sg of 1.0243. The only time density = Sg is at 4 C or using a 4C hydrometer at 25 C then Sg = Density = 1.0234


Other cond to ppt calculators

http://www.fivecreeks.org/monitor/sal.html

53,065 uS = 35 ppt

http://www.marscigrp.org/ocean.html

52,998 uS = 35 ppt

http://www.ultrasw.com/alcock/creeks/sal.shtml

53,065 uS = 35 ppt


http://fermi.jhuapl.edu/denscalc.html

5.3065 S = 35.000173


http://www.americanmarineusa.com/salinityconversion.html

53 mS+ 35 ppt. Don't be misled by the Sg, as it is a 20 C hydrometer and not at 25 C.

http://www.hamzasreef.com/Contents/Calculators/ResultingSalinity.htm

53.065 mS = 35 ppt


http://fermi.jhuapl.edu/denscalc/fofonoff_millard_1983.pdf




Take note of the author Dr. Frank Millero. Fell free to call, write or e-mail him at the University of Miami and ask him the question will the off-set for different ASW ( and he plays with lots of them) mean anything in conductivity, sg relationship conversions.

http://www.rsmas.miami.edu/divs/mac/faculty/fmillero/fmillero.html



Some things to read

Reef Aquarium Salinity: Homemade Calibration Standards
http://www.reefkeeping.com/issues/2004-06/rhf/index.php

Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/index.php

Using Conductivity to Measure Salinity
http://www.aquariumfish.com/aquariumfish/detail.aspx?aid=1804

What is TDS?
http://www.reefkeeping.com/issues/2004-04/rhf/feature/index.htm
 
Last edited:
Much to read. My personal conclusion:
We add the option to "calibrate" (add an offset) in our firmware
Maybe not 100% scientific, but pragmatically.
 
<a href=showthread.php?s=&postid=12830511#post12830511 target=_blank>Originally posted</a> by jansenwrasse
Don't assume anything ... it will only get you in trouble ... I assumed Boomer liked me ;)
Click to expand...
WOW you need to come to meetings he can learn!!!!!:rollface:

Jim
 
Go Back to your hole Jim;) But Jansen was correct, he assumned I liked him and do :D
 
Conductivity in saltwater solutions is measured in Siemens, thus the mS numbers. It's usually given corrected to a specific reference temperature, since raw conductivity varies with temperature. For ocean water, the usual reference is 25 C.
 
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