Refractometer Calibration

[Meadowlark]

Can I use tap water for the calibration of my refractometer? It recommends distilled water. Will this make a difference?

 

[SeanT]

No you can not.
Yes it will make a HUGE difference.

Tap water has a lot of minerals in it, which, ARE "dissolved solids".

 

[sjm817]

Neither. You need to calibrate it with a SW solution.

 

[SeanT]

Definitely.
Distilled or RODI water will give you a reading of 0.
You can buy packets of calbration solution so you can test that end as where a known result can be expected.

 

[drummereef]

Don't use RO/DI water for calibration. It is innacurate. Use the method described in this article.

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

 

[bertoni]

The PinPoint 53 mS salinity calibration solution is also useful for calibrating refractometers.

 

[cmaki]

Distilled water.

 

[Travis L. Stevens]

Definitely a calibration solution. Calibrating with freshwater can lead to large errors. I once had a refractometer calibrated with freshwater, and when it read full strength saltwater at 1.025, it was actually 1.019

 

[kevin2000]

Distilled water will work fine.

 

[sjm817]

<a href=showthread.php?s=&postid=10186533#post10186533 target=_blank>Originally posted</a> by kevin2000
Distilled water will work fine.

It may work fine IF you have a refractometer that has a perfectly linear scale. Many do not, which is why you need to calibrate it with a standard close to the intended test value, which is not distilled water..

 

[kevin2000]

<a href=showthread.php?s=&postid=10186565#post10186565 target=_blank>Originally posted</a> by sjm817
It may work fine IF you have a refractometer that has a perfectly linear scale. Many do not,

That may be true ... however the three refractometers I have owned over the yrs have all recommended calibration with distilled water. I have no doubt that the majority of refractometers sold to SW enthusiast can be calibrated with distilled water.

 

[sjm817]

The problem is many people including myself are not so lucky. Calibrating with RO proved to be .003 - .004 off on the measurement that actually matters. Its been proven as fact many times now that calibration with RO is not a good idea despite what a mfgr claims.

So I guess it depends if you want to trust/assume you have a refractometer that is accurate @ 1.026 that is calibrated @ 1.000.

You may want to read this:

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

 

[kevin2000]

<a href=showthread.php?s=&postid=10186759#post10186759 target=_blank>Originally posted</a> by sjm817
Calibrating with RO proved to be .003 - .004 off on the measurement that actually matters. Its been proven as fact many times now that calibration with RO is not a good idea despite what a mfgr claims.

I have never recommended using RO water to calibrate a refractometer .. and you should note there is a big difference between RO water and distilled water. When I lived in the Midwest with super lousy tap water the RO water was still worse than the tap water in Portland Oregon (needed to add DI). To my knowledge no refractometer mfg recommends using RO.

 

[sjm817]

Moot point. Either way, you are calibrating @ 1.000. If you want to be sure your refractometer is accurate for testing FW, RO or distilled are fine calibration standards. If you want to calibrate it for SW testing, they are not.

I assume you did not read the article by Dr Randy-Holmes Farley that explains why this is the case.

 

[Travis L. Stevens]

Kevin, two things here. If you read the label on Distilled water, you'll see that it goes through an RO process as well as distillation. In addition, nearly all available refractometers intended for aquarium use are actually brine refractometers and not seawater refractometers. The refractive index between brine and seawater are different. Calibrating these refractometers with freshwater will give very accurate readings for measuring brine water, but not when you are measuring seawater.

 

[kevin2000]

I don't think the point is mute at all .. there is a big difference between using tap water, RO water, and distilled water. Further .. I have used calibration fluids before noting my wallet size went down without making a noteable difference in the accuracy of the refractometer.

 

[bertoni]

Refractometers can have various problems when calibrated with fresh water, as the article describes, so I wouldn't trust that method. In most cases, I think it works well enough, though. The question then is, how much risk do you want to take.

 

[sjm817]

I spent a whopping $3.50 on salinity calibration fluid, which showed that my refractometer was off by .004 when calibrated with RO to 1.000. I dont see why anyone would just assume the refracto is accurate for testing SW when calibrated with FW. It may be, it may not be. The whole reason you calibrate to begin with is to take the guesswork out of the equation.

 

[seagirl]

use this

http://www.diyreef.com/shop/product_info.php?cPath=70&products_id=36

it's $3, you have to use a calibration fluid, not water.

 

[ambaratur]

<a href=showthread.php?s=&postid=10187064#post10187064 target=_blank>Originally posted</a> by seagirl
use this

http://www.diyreef.com/shop/product_info.php?cPath=70&products_id=36

it's $3, you have to use a calibration fluid, not water.

Interesting - on that site they call PPT as parts per trillion. I am pretty sure that the correct measure is parts per thousand. Would worry me about buying a "lab grade" product that is mislabeled.

just my opinion though.