Salinity madhouse

Coffeeinbed · 07/29/2014, 03:37 PM

My el-cheapo RHS 10ATC refractometer says something different than both my swing-arm (Corallife) SG meters and I don't know what to trust.

Does anyone use the RHS 10ATC?

Refractometer tested using - http://reefkeeping.com/issues/2004-06/rhf/index.php

test solution - 35ppt - Mortens salt and distilled water - 5 ( 6.2g + 161g)

Refractomter says 35.5 after 2 full minutes of waiting (rather than 30sec).

tkeracer619 · 07/29/2014, 03:40 PM

take it to the lfs and compare.

Ontheway · 07/29/2014, 03:58 PM

Test with 0 tds rodi water, in an air conditioned room to see it stays@1000 in 2min, (a sharp line, not a fuzzy one), then go from there. Using the same refract. It's best to calibrate them @20 degrees celcius.

Edit: swing arms are only good for having a rough idea on salinity, ie, whether Sal. is way off or not. Other then that, they are basically toys.

tkeracer619 · 07/29/2014, 04:10 PM

Funny thing about toys.

They can be better than more accurate tools that suffer from poor calibration.

I wouldn't calibrate a refractometer with water. You want a 35ppt calibration fluid.

Ontheway · 07/29/2014, 04:15 PM

The best is two point calibration, but under appropriate conditions, rodi water calibration is ok, did it on same unit, then checked with 35ppt, it was razor sharp on 35.

kurt_n · 07/29/2014, 05:33 PM

Quote:

Originally Posted by Ontheway

The best is two point calibration, but under appropriate conditions, rodi water calibration is ok, did it on same unit, then checked with 35ppt, it was razor sharp on 35.

Problem is, not all refractometers will calibrate like that. My first one did; second one... not so much.

And unless you have the 35ppt solution, you don't know if yours is one of the lucky ones.

So if you need the 35ppt solution to verify... why not just use it to calibrate!

If you can only do a single point calibration (like just about all our refractometers) it's best to calibrate it to something close to what you're trying to measure.

As far as the original question... I'd trust a refractometer calibrated with 35ppt solution over any swing-arm, anytime.

Coffeeinbed · 07/29/2014, 06:48 PM

Thanks for the input guys....

Can anybody recommend a refactometer ( a resonably priced one)?

I had the swing arms on-hand so I could see if anything was waaaay off - an alarm bell of sorts. But when all instruments read differently on the same sample what you get is madness...no information at all.

kurt_n · 07/29/2014, 09:06 PM

Quote:

Originally Posted by Coffeeinbed

...
I had the swing arms on-hand so I could see if anything was waaaay off - an alarm bell of sorts. But when all instruments read differently on the same sample what you get is madness...no information at all.

If "all instruments" means the swing arms and the refractometers, it's not gonna happen. If you're expecting swing-arms to read the same as a calibrated refractometer, I think you're expecting too much. It's like looking at three different thermometers and trying to figure out which one is "right".

Go by the refractometer.

mussel and hate · 07/29/2014, 10:23 PM

some of us have been succesfully using the same swing arm hydrometer for 25 years. calibration is key regardless of device. calibrate for 35ppt.

Ontheway · 07/30/2014, 02:07 AM

Do not think swingarms has ATC feature. You don't need another ref., either. Just make a two point calibration, this is all you need. Even if you buy another brand, you will still need to find 35 ppt fluid.

kurt_n · 07/30/2014, 08:48 PM

You can't do a true two point calibration with refractometers... at least hobby-grade ones.

Two point calibration means your are adjusting both the "zero" and the "slope" of the instrument. The calibration screw of refractometers just adjusts the "zero"... there's no way of adjusting the slope.

So wherever you calibrate it (or "zero" it) that is where you are guaranteed it is accurate. It *may* be accurate in other places also, but it's not a guarantee.

And I'm not saying *all* swing arm hydrometers aren't accurate. I'm just saying I'd trust a refractometer over a swing arm every time, just due to the ease of repeatability and calibration.

07/29/2014, 03:37 PM	#1
Coffeeinbed Registered Member Join Date: May 2014 Posts: 182	Salinity madhouse My el-cheapo RHS 10ATC refractometer says something different than both my swing-arm (Corallife) SG meters and I don't know what to trust. Does anyone use the RHS 10ATC? Refractometer tested using - http://reefkeeping.com/issues/2004-06/rhf/index.php test solution - 35ppt - Mortens salt and distilled water - 5 ( 6.2g + 161g) Refractomter says 35.5 after 2 full minutes of waiting (rather than 30sec).

07/29/2014, 03:40 PM	#2
tkeracer619 Registered Member Join Date: Jan 2006 Location: Westminster, CO Posts: 17,289	take it to the lfs and compare. __________________ Hobby Experience: 9200ish gallons, 26 skimmers, and a handful of Kent Scrapers. Current Tank: Vortech Powered 600G SPS Tank w/ 100gal frag tank & 100g Sump. RK2-RK10 Skimmer. ReefAngel. Radium 20k.

07/29/2014, 03:58 PM	#3
Ontheway Registered Member Join Date: Oct 2013 Posts: 412	Test with 0 tds rodi water, in an air conditioned room to see it stays@1000 in 2min, (a sharp line, not a fuzzy one), then go from there. Using the same refract. It's best to calibrate them @20 degrees celcius. Edit: swing arms are only good for having a rough idea on salinity, ie, whether Sal. is way off or not. Other then that, they are basically toys. __________________ Low ph, high kH... what can I do now?

07/29/2014, 04:10 PM	#4
tkeracer619 Registered Member Join Date: Jan 2006 Location: Westminster, CO Posts: 17,289	Funny thing about toys. They can be better than more accurate tools that suffer from poor calibration. I wouldn't calibrate a refractometer with water. You want a 35ppt calibration fluid. __________________ Hobby Experience: 9200ish gallons, 26 skimmers, and a handful of Kent Scrapers. Current Tank: Vortech Powered 600G SPS Tank w/ 100gal frag tank & 100g Sump. RK2-RK10 Skimmer. ReefAngel. Radium 20k.

07/29/2014, 04:15 PM	#5
Ontheway Registered Member Join Date: Oct 2013 Posts: 412	The best is two point calibration, but under appropriate conditions, rodi water calibration is ok, did it on same unit, then checked with 35ppt, it was razor sharp on 35. __________________ Low ph, high kH... what can I do now?

07/29/2014, 06:48 PM	#7
Coffeeinbed Registered Member Join Date: May 2014 Posts: 182	Thanks for the input guys.... Can anybody recommend a refactometer ( a resonably priced one)? I had the swing arms on-hand so I could see if anything was waaaay off - an alarm bell of sorts. But when all instruments read differently on the same sample what you get is madness...no information at all.

07/29/2014, 10:23 PM	#9
mussel and hate Registered Member Join Date: Aug 2011 Location: location location Posts: 701	some of us have been succesfully using the same swing arm hydrometer for 25 years. calibration is key regardless of device. calibrate for 35ppt.

07/30/2014, 02:07 AM	#10
Ontheway Registered Member Join Date: Oct 2013 Posts: 412	Do not think swingarms has ATC feature. You don't need another ref., either. Just make a two point calibration, this is all you need. Even if you buy another brand, you will still need to find 35 ppt fluid. __________________ Low ph, high kH... what can I do now?

07/30/2014, 08:48 PM	#11
kurt_n Registered Member Join Date: May 2006 Location: WA Posts: 2,592	You can't do a true two point calibration with refractometers... at least hobby-grade ones. Two point calibration means your are adjusting both the "zero" and the "slope" of the instrument. The calibration screw of refractometers just adjusts the "zero"... there's no way of adjusting the slope. So wherever you calibrate it (or "zero" it) that is where you are guaranteed it is accurate. It may be accurate in other places also, but it's not a guarantee. And I'm not saying all swing arm hydrometers aren't accurate. I'm just saying I'd trust a refractometer over a swing arm every time, just due to the ease of repeatability and calibration.