Salinity readings on Refractometer Vs. Controller

[Green_Lionfish]

I've been trying to get 1.025 salinity, but the readings from refractometer and Apex controller is different. Refractometer says 1.025, apex says about 1.023. Both of them have been calibrated.

Which one should I go with as reference?


Thanks

 

[MARINECRITTERS]

I personally go with a hand held refractometer, they are less gimmicky and in my opinion give better results.

 

[GratefulReef]

I'd go with 1.024 its the only one they didnt guess lol...honestly I'm not sure but prob the refractometer as its only job is to do that where the apex is meant to do many other things, so more chance for error maybe

 

[shonc182]

If both both have been calibrated, I would go with the refractometer.

 

[Painted skin]

+1 Refractometer

 

[Fgtank]

+ 1 refractometer

 

[disc1]

How were they calibrated? If you only zeroed the refrac with RODI then I'd lean towards the conductivity meter.

 

[Recliner]

How were they calibrated? If you only zeroed the refrac with RODI then I'd lean towards the conductivity meter.

But if the calibration fluid was used?

 

[worm5406]

Was the temperature the same of the calibration fluid and the tested water?

 

[Sonyardo]

As long as it was properly calibrated then I would go with the refractometer.

 

[OregonReefer2]

Was the temperature the same of the calibration fluid and the tested water?

Doesn't matter. The temp of the couple drops of either on the refractometer will quickly (within 2-3 seconds) adjust to the temp of the meter.

If you're concerned about the minor salinity difference from temp you need to have the meter at the temp you want to test at

 

[GroktheCube]

They were both calibrated with 35ppt calibration solution?

Have you checked the conductivity probe in calibration solution again?

I'd tend to trust the refractometer over the probe, though both should be good if calibrated properly. That's a pretty big difference, so one of the two devices is definitely faulty, assuming they were freshly calibrated.

 

[shonc182]

Worth mentioning - The instructions I had with my Apex probe said that with the 53.0 ms solution, it cannot be used to calibrate a refractometer. The composition is not the same as saltwater and will not show 35.0

 

[OregonReefer2]

Worth mentioning - The instructions I had with my Apex probe said that with the 53.0 ms solution, it cannot be used to calibrate a refractometer. The composition is not the same as saltwater and will not show 35.0

There's a thought... If the refractometer was calibrated with Apex probe calibration solution it could be off by a great deal

 

[fishgate]

Get a third opinion. Borrow a refractometer from somewhere - or buy another one.

 

[Dave & Monica]

I crossed this bridge with Neptune awhile back. Although this article talks to why the probe is better. I agree with most everyone here, and personally trust my refractometer more.

http://************.com/2010/07/12/dd-seawater-refractometer-scaled-calibrated-seawater-saltwater/


From Neptune "It explains the 2 to 3 ppt difference between the salinity reading of a
refractometer and a conductivity meter. The cond. meter (ours in
particular) is the one that is right."

 

[d2mini]

Same with Profilux. I alway tend to get a slightly lower reading with the probe vs the refractometer. How is your probe coming up with the salinity reading? Does it give you an mS reading? Have you tried to find two online mS-salinity converters that give the same results? The apex is probably converting from one to the other and without a true industry standard you'll have a variance. Can you get a mS reading on the apex, do the conversion and see if it's different?

I get an mS reading of 49.3 right now on my Profilux, and using this conversion i get 1.0243.
http://www.hamzasreef.com/Contents/Calculators/SalinityConversion.php
My refractometer says 1.026
But if I use the Profilux internal conversion, choosing to display density, it gives me a reading of 1.0225.
This is because there is no industry standard for the conversion.

btw, you may also want to clean the probe. Mine needs almost constant cleaning, maybe because its near a light source. It's been a couple weeks since i cleaned so my current reading may be a little low. If I clean it I might get a bit closer to the refractometer reading.

 

[thegrun]

Doesn't matter. The temp of the couple drops of either on the refractometer will quickly (within 2-3 seconds) adjust to the temp of the meter.

If you're concerned about the minor salinity difference from temp you need to have the meter at the temp you want to test at

Temperature has a greater effect on a conductivity probe than a refractometer, so the temperature of the calibration solution is critical when adjusting the conductivity probe. Ideally the thermometer should also be submerged in the calibration fluid.

 

[pjewett]

Well this article settles it for me. Having been considering adding the salinity probe to my Apex but was suspicious. Saved me some money.

 

[AJsTank]

Get a third opinion. Borrow a refractometer from somewhere - or buy another one.

Agreed. Get a 3rd opinion. Also, how old is your probe? A rep from Apex told me I should replace my probe every 12-18 months. I know people who have kept their for 2-3 years and it seems okay.