Looking to purchase refractometer

[SPS]

I much prefer to use my box swing arm hydrometers that I keep clean with white vinegar and rinse after every use.
I calibrated them against my certified calibrated Fisher Scientific hydrometer and cut material off the swing arm to lower the reading for one, and cut material off the weight material to bring the reading up on the other one.
I only check the boxes against the certified hydrometer once a year and find daily use of the box to be quite convenient.
At a club meeting last year, nine refractometers, some the same brand, gave readings up to 3ppt different even though the owners swore to the calibration of their unit.
I've used my certified calibrated hydrometer to check other hobbyists swing arms but the newer ones we just mark the variation on the plastic hydrometer because the newer ones don't come apart to adjust like the old ones did.

I have always had issues with hydrometers, even calibrated ones. The problem is, i think, they are calibrated at a certain salinity, so the readings for any other salinity wasn't perfectly accurate.

Though, I put that behind me a got a digital salinity meter.

 

[rayjay]

A certified calibrated hydrometer will not be inaccurate.
Any inaccuracy would only be because of someone using it that doesn't understand how.
I would bet on my hydrometer over your refractometer. It doesn't depend on needing calibrated after the initial factory calibration and home calibration of refractometers can be a crapshoot as store bought calibration fluids are not always exact.
(I'm not talking about a hobby hydrometer, but rather my Fisher lab hydrometer that I check my hobby ones against)
The charts that come with the hydrometer are accurate so there is no problem there.
You can even cool the water down to 60°F (using a lab thermometer) and verify your results if you really don't trust it.

 

[Boomer]

have always had issues with hydrometers, even calibrated ones. The problem is, i think, they are calibrated at a certain salinity, so the readings for any other salinity wasn't perfectly accurate.

That is true, you need to know the calibration temp. Once you know that then use this calculator for FLOATING hydrometers. The numbers in the link below are only examples. You can Change them by just typing them in.

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

Swing arm hydrometers are another issue, as some use thermal expansion plastic which auto correct for temp but others may not. For sure the Instant Ocean one is auto correct. The issue for most with swing arms is users do not keep them clean, where salt deposits build up on the arm and weigh it down giving false low readings.

And I stand behind rays' remarks as far a refracts used in this hobby.

However, with the proper solution they are good for a narrow range of Salinity but NOT for a FULL range of Salinity like a lab hydro. Reason, all refract that are hand-held are set to a NaCl std and seawater is not NaCl. A 35 ppt NaCl does not give the same RI as 35 ppt NSW. Finally, for refracts, even the cheap ones in this hobby are close enough for reef salinity ranges. If one wants to get knit picky about accuracy then nothing is more accurate than a conductivity meter, if you have ~ $400 or more to spend. Scientific research on seawater is only with a conductivity meter, which is the std for seawater salinity measurement.



For further reading

Salinity

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

Specific Gravity Measurement
http://www.advancedaquarist.com/2002/1/chemistry

Temperature Corrections for Hydrometers
http://reefkeeping.com/issues/2004-07/rhf/index.htm

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

 

[cyberdeth]

New toys/tools are sweet! Really quick shipping! Thank you Boomer/Filter Guys!!!

 

[SPS]

have always had issues with hydrometers, even calibrated ones. The problem is, i think, they are calibrated at a certain salinity, so the readings for any other salinity wasn't perfectly accurate.

That is true, you need to know the calibration temp. Once you know that then use this calculator for FLOATING hydrometers. The numbers in the link below are only examples. You can Change them by just typing them in.

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

Swing arm hydrometers are another issue, as some use thermal expansion plastic which auto correct for temp but others may not. For sure the Instant Ocean one is auto correct. The issue for most with swing arms is users do not keep them clean, where salt deposits build up on the arm and weigh it down giving false low readings. ~~REDUCED~~

A certified calibrated hydrometer will not be inaccurate.
Any inaccuracy would only be because of someone using it that doesn't understand how.
I would bet on my hydrometer over your refractometer. It doesn't depend on needing calibrated after the initial factory calibration and home calibration of refractometers can be a crapshoot as store bought calibration fluids are not always exact.
(I'm not talking about a hobby hydrometer, but rather my Fisher lab hydrometer that I check my hobby ones against)
The charts that come with the hydrometer are accurate so there is no problem there.
You can even cool the water down to 60°F (using a lab thermometer) and verify your results if you really don't trust it.

Yes, and no. I am sure some are accurate, but from personal experience, I've never had one that was accurate, even after proper cleaning.

 

[rayjay]

First of all, I suspect you've never had a CERTIFIED hydrometer. A certified hydrometer only needs to be kept properly cleaning to be capable of producing a true reading.
How would one know if a hydrometer is reading correct?
If you use a certified hydrometer CORRECTLY and get a different reading from a hobby refractometer, then the refractometer is the incorrect reading.
The only way to be sure the hobby refractometer is calibrated correctly is to check the reading against a conductivity meter but a certified hydrometer will give you a pretty darn good idea if it is out of calibration even a little.
I have seen calibration fluids sold for laboratory use that were not good enough to properly calibrate a refractometer.
As for swing arm hydrometers, once you check the calibration on a swing arm hydrometer, then all you need to do is maintain it correctly and it should give you good service, again, if it is used correctly.
It makes an easy quick check to see if your range is troublesome, at least in the range it has been checked for.

 

[Boomer]

You have seen a certified hydrometer being inaccurate, as that is what your post implies ? I do no but that at all. In my 40 years of playings with these things I have never seen a certified hydrometer inaccurate yet. Maybe it is your digital Salinity meter that is inaccurate. Who's do you have and how do you calibrated it.

As far as floating hydrometers go, by IO, many have been tested in labs by me an others and all have found them fairly accurate but not exact, using a $1,000 conductivity meter. Usually they read a tad low but are within their spec's of +/- 1 ppt. Al least 95 % of the time when it comes to any hydrometer it is user error.

 

[rayjay]

Geez Boomer, you sound like you're as old as I am!:lol:

 

[Boomer]

62 years old

 

[rayjay]

Well if I pass on tonight, it'll take you another 6 years to catch up!
Another 17 years and I'll be an old man.