Hydrometer test

[Limpit]

After finding out about 6 months ago that my old (20 years plus years) SeaTest hydrometer was no longer accurate by a long shot I purchased a Coralife Deep Six hydrometer. I did not like the fact that the Deep Six had a very narrow base and could tip over easily. So I then went out and bought an Instant Ocean brand hydrometer. After reading a lot of posts about how inaccurate the swing type hydrometers are I purchased one of Foster and Smiths $40 refractometers.
After receiving my refractometer and checking the salinity of my water with it I was shocked to find that it was much different that what my float arm hydrometers were saying it was so I decided that I would document a side by side comparison and share it with everyone.

A little background on what I did:
All of the water used came from the same tank at the same time. I used a small container to dip some water out of my tank. That water is what I used for the testing.
All of the hydrometers were “seasoned� as the instructions on their packages said.
All hydrometers were rinsed before and after use and before the readings were taken any excess fresh water from the rinse was removed.
Test water was added to each unit and I made sure that all bubbles were removed and allowed the hydrometer to sit for a minute or so before the readings were taken.

This is what I found:
http://img.photobucket.com/albums/v358/Limpit/Deep6.jpg
Picture 1 shows the Coralife Deep Six with a reading of 1.0195

http://img.photobucket.com/albums/v358/Limpit/IOlarge.jpg
Photo 2 shows the Instant Ocean brand with a reading of about 1.027

http://img.photobucket.com/albums/v358/Limpit/Seatest.jpg
Just for kicks I tested the water with my ancient SeaTest unit and it read 1.018

I then tested the water with my refractomer and it showed a specific gravity of 1.024

While I am no lab expert what I had found was that there is a wide range of readings by the various hydrometers. If the refractometer is the most accurate way to test your salinity than I would say that the Instant Ocean brand hydrometer was closest to the refractometers reading.

Just thought you would be interested in reading this.

[maxvan1]

whoa... I need a refractometer...

[Nuhtty]

Refractometers are the way to go.

$35.00...cant beat that. You may save that money in salt alone if you find out you arent mixing your water to the proper salinity.

Of course, one good coral or one good fish that doesnt appreciate the mistakes in salinity will reach that $35.00 mark as well

[drjrose]

Originally posted by Limpit
I would say that the Instant Ocean brand hydrometer was closest to the refractometers reading.

You might run that test again daily for a few days and see what the variances are.

[Limpit]

Originally posted by drjrose
You might run that test again daily for a few days and see what the variances are.
Good idea, I'll do that.

[Limpit]

Originally posted by maxvan1
whoa... I need a refractometer...
I was very pleased with the $40 one that I got from Foster and Smith. It even came with a hard case, calibration screw driver and a small pipette.

[reverai]

I should also point out my Deep Six hydromete match has matched my refractometer test 123 out of 125 times. I clean the hydrometer with distilled water and vinegar once a week and I doubt many people do that which might make a difference.

Steve

[Limpit]

Originally posted by drjrose
You might run that test again daily for a few days and see what the variances are.
As requested I did a follow up test to see if there were any changes, here is what I found.

Refractomer: 1.025
Coralife Deep Six: 1.020
Instant Ocean: 1.0235
and my 20 plus year old SeaTest: 1.018

While according to my Refratometer salinity went up .001 the Deep Six was the only one to show an increase. The Instant Ocean went down and the SeaTest stayed the same.

To answer the statement made by reverai, I also do clean my hydrometers after every use with water from my RO.

I wonder if some one from either Marine Labs or Coralife reads this board could comment on this topic?

[reverai]

Interesting. I guess there is some variation with the hydrometers. I should mention that hydrometers were used since the 1700s and the
principlethey use to work has been around for quite a while. I remember making my own hydrometer back in high school chem class and it worked well or I wouldn't received a A in the class. I know my hydrometer is right on as I do test my water with both the hydrometer and refractomer.

Steve

[The Punisher]

I've seen enough threads about people with bad hydrometers to think that they work well even close to most of the time. I used one for the first few months but switched to a refractometer. I do the side by side test every now and then and the hydrometer is always very close to the refractometer, but I would say that this is rare. In this hobby $40 for piece of mind is worth it. Yes, some hydrometers work but it seems the majority of them don't.

[god_of_wolves]

With something as important as salinity... There is no point in going the cheap route on this one.