Refractometer calibration?

[sondaar]

HEy all this may be a dumb question but I have a Vertex Refractometer and the directions say to calibrate with fresh water. I bought a bottle of Pinpoint Salinity solution to check it with. When calibrated to 0 with fresh water the solution reads 38ppt. The solution is suppose to read 35ppt. Is it better to use the solution for calibration or stick with the directions and use fresh water?

Thanks!

 

[Sisterlimonpot]

Use the solution. Are you using tap water or distilled water from the grocery store?

 

[sondaar]

Im using RODI water from my unit.

 

[Reef_Matrix29]

if you are using RODI water to set your "zero" endpoint and then your stock solution is reading 38 ppt, it is possible that the solution is reading high or actually is 38 ppt. there are bad batches of chemical solutions all the time, the important thing is consistentcy amongst the readings to ensure that your refractometer isn't busted

 

[sue711]

I calibrate with pinpoint solution even though my instructions say to use distilled.

 

[abulgin]

<a href=showthread.php?s=&postid=15401971#post15401971 target=_blank>Originally posted</a> by wesley6610
if you are using RODI water to set your "zero" endpoint and then your stock solution is reading 38 ppt, it is possible that the solution is reading high or actually is 38 ppt. there are bad batches of chemical solutions all the time, the important thing is consistentcy amongst the readings to ensure that your refractometer isn't busted

It's much more likely that the RO/DI calibration is off by 3 ppt than it is that the Pinpoint solution is off. You should always calibrate using the Pinpoint solution, and never RO/DI unless you're in a pinch.

 

[Reef_Matrix29]

I would agree that if you have a reliable solution to use that, but don't develop an over reliance on any one product. Here at the state lab we use a lot of vendors for our pH meters and bulk supplies for random quality testing, they don't always meet their specs and Q/A claims. I'm sure that if you find a good one for your refrac meter that you should stick with it.

 

[abulgin]

Keep in mind that even though your TDS meter says your RO/DI water has 0 ppm of TDS, it's probably not 100% accurate. The Pinpoint solution is top-notch. Sure, there will be bad batches with anything now and then, but I would trust Pinpoint over my RO/DI any day.

 

[Reef_Matrix29]

I would agree with abulgin

 

[MotherFish]

It sounds like your refractometer has a slope miscalibration.

Randy Holmes-Farley did an extensive article on refractometers and calibration in the Dec. '06 issue of Reefkeeping magazine.
http://reefkeeping.com/issues/2006-12/rhf/index.php


Personally I would get a second bottle of Pinpoint solution to double-check the results from the original bottle for peace of mind.
At $5-7 for a bottle, it's one of the cheapest investments you'll make in this hobby, and if you find they are both reading the same then you can sell the extra bottle to a fellow reefkeeper in your local club or area.

 

[Reef_Matrix29]

Now that sounds like an excellent idea and wouldn't hurt to have a second opinion to verify wether your solution is the culprit or not!

 

[snorvich]

<a href=showthread.php?s=&postid=15402513#post15402513 target=_blank>Originally posted</a> by abulgin
It's much more likely that the RO/DI calibration is off by 3 ppt than it is that the Pinpoint solution is off. You should always calibrate using the Pinpoint solution, and never RO/DI unless you're in a pinch.

Agreed.