My hydrometer specification..?

[elisabeth]

i went and measured some fresh NSW and it read 1.016
Someone asked if the hydrometer was calibrated.. well
i went and measured plain tap water and this is what
it reads:
http://img78.photobucket.com/albums/v243/elisabethdrooling/hydrometer_h2o.jpg
So it appears *less* than 1.00?? So i read the specification
and it says ASTM 1111, do i hvae the wrong hydrometer for
saltwater and if so, is there a conversion formula for it?
Here's a pic of the designation:
http://img78.photobucket.com/albums/v243/elisabethdrooling/hydrometer_spec.jpg

many many thanks for your help in this!!

[NicoleC]

Hydrometers are poor instruments. "Calibration" is not really a firm concept with them. If you want to get a good idea of where your hydrometer stands, you need to compare it to a refractometer.

But really, just buy the refractometer. You'll never believe you put up with a hydrometer! I see refractometers for $100+ in LFS, but I bought the same one on eBay for $40. I'm not one for gadgets, but this one is near indispensible.

[elisabeth]

i have to disagree with that. When i was purchasing this one--
'armed with a little knowledge'....:), i saw certified hydrometers
that had been calibrated blah blah blah, it's jsut that i think
i chose the wrong one for what i'm measureing--saltwater.
As an aside, i've used this thing for several years now and
the tank seems fine, so if anything it shows the ability of most
things to adapt--it would also explain why none of my long
spine urchins ever made it through an acclimation:( but
who knows.. Perhaps the good doctor? :)

[rshimek]

[moved]

[elisabeth]

for clarification, i should say that while the picture
has it stuck to the side of the cylinder-duh--it reads
pretty much the same when it's properly suspended
in the liquid.

[Boomer]

Lis

What you have is a HYDROMETER, ASTM 111H #35125-647 sold by www.vwr.com. The hydrometer is made buy H-B Instrument Company www.hbinstrument.com and it should not read what it is reading, as far as I'm concerned. I gave them a call, the guy is out, he will call me tomorrow hopefully. I can clearly see it goes below 1.000 but the girl I talked said no, its range is 1.00-1.050. It looks like the unit is off by .0005 units, at a glance or 1.016 = .0005 = 1.021. If that water sample was @60 F, like it says on the hydrometer = 27 .5 ppt @ 60F. If the water temp was 82 F and we corrected = 31.7 ppt, which sounds correct if you didn't add quite enough salt. Often if you follow the instructions on some bags this is about what you get. But all this is just a guess, we need to wait for an answer from HB. What is the serial # on the side I can't read it, I may need it. And no you don't have the wrong, one according to them but something is funny :D

Nicole

Hydrometers are poor instruments. "Calibration" is not really a firm concept with them. If you want to get a good idea of where your hydrometer stands, you need to compare it to a refractometer.

This is very incorrect, they are very accurate as long as they are corrected for temp. As far as that "comparing to a refractometer", they are off .015 units SG or 1.5 ppt right out of the box, as they are not calibrated to seawater but NaCl soluton. NaCl and seawater DO NOT have the same RI (Refractive Index). Randy and I spent allot of time looking for and collecting data, so he could write this.

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

Here are somemore related articles

Specific Gravity: Oh How Complicated!
http://www.advancedaquarist.com/issues/jan2002/chemistry.htm


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

[Boomer]

Typo, that should be .005 not .0005

[Randy Holmes-Farley]

That hydrometer is designed to be used at 60 deg F. Fresh water at temperatures above 60 deg F will read lower than 1.000000. What temperature was the water (tank and fresh?)

My article this month may be timely:

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

[elisabeth]

the serial # is 223739

the tap water temp.--taken jus now is 29C
warm i know--but when i first bought it i put
the cylinder of water in the fridge to get 60F--
not real easy to do BTW--and it was still below 1.0000

[Randy Holmes-Farley]

How much below when it was 60 deg F?

[Boomer]

Lis

I talked to Dave at HB. First, is there a RED mark on the hydrometer centered at the 1.0000 mark ? I don't see it in the pick but it may be on the back side. When you cool a sample down in frig you must make sure the water temp is the same through-out the cyclinder. If the water in the cyclinder is colder at the top than further down it will make the hydrometer sink more. You need to be sure the salt mix is also at a constant temp through-out. When you tested the seawater what temp was it, 60 F ? And yes, this company often has marks on the hydrometer below the 1.000 like yours. Dave thinks there may be something wrong with this unit, he is just checking to make sure. Dave suggests to bring it back from where you got it, VWR I would presume. You could also call Dave and talk to him if you like. 1-610-489-5500 or toll free at 800-4 TEST-Lab.