View Full Version : Do Not Trust Hydrometers!

12/22/2006, 09:10 PM
DO NOT TRUST HYDROMETERS. IN MY EXPERIENCE THEY ARE ALWAYS INACURATE. I have never bought one that was accurate. I once bought one that read 1.025 when the actual specific gravity was 1.035. I have four other hydrometers and they are all off by an unacceptable amount. Don't put your corals and fish at jepordy. Spend the extra 20 bucks and get a refractometer. If you don't like using a refractometer all the time, you can always callibrate your hydrometers by using a refractometer. Just put + or - the amount it is off on the hydrometer with a permanent marker.

12/22/2006, 09:14 PM
Did no one warn you before?

12/22/2006, 09:22 PM
I learned this lesson a long time ago. I just wanted to warn any newbies.

12/22/2006, 10:37 PM
I had a swing arm unit that I didn't trust, so I bought a refractometer. Turns out that the hydrometer was DEAD ON all along. Just my luck! :mad:

12/22/2006, 10:52 PM
I didn't trust one the first time I bought one. 5 seconds for a quick search, and bam, ordered my first refractometer. (That was back when you could perform a search on Reefcentral)

12/22/2006, 11:11 PM
Make sure you calibrate a refractometer against a solution of known salinity, instead of just calibrating to zero with pure water. Many of the cheaper blue handled refractometers are quite inaccurate unless calibrated in the ranges we use them for (1.020-1.026). Don't automatically assume a refractometer is more accurate unless you first check the accuracy of the refractometer.

12/22/2006, 11:34 PM
I have just tested two different refractometers and they are both way off. I have a known 35ppt salinity standard and after calibrating both refractometers to distilled water one tested to 32ppt and the other to 40ppt. I then calibrated them to the salinity standard of 35ppt. One showed my tank water at 1.0257 and the other was at 1.030. My swing arm hydrometer reads 1.0245 and my conductivity meter reads 1.0256. One refractometer is a new $80.00 Milwaukee and the other is a $40.00 cheepo. I don't know what to make of this , I'm determined to get to the bottom of it. I was trying to buy a high quality meter. It should be able to calibrate on distilled water at 0 and read the salinity standard of 35ppt accurately. I will have to wait to contact Milwaukee after Christmas to see what they say. I'm tired of guessing what my salinity is, there is too much time and money involved to guess.
Merry Christmas

12/23/2006, 12:04 AM
WOW, I didn't know this. I was lead to believe that a hydrometer was theeee method of accurately reading salinity but it was just a hassle. Now I am wondering what I have been putting my coral and fish through.

pfish I will be watching closely what you have to report from milwaukee and then place an order for a quality refractometer. Dang the list of things that I think I know but don't really just keeps getting longer the older I get.

12/23/2006, 12:10 AM
You got that right. I will keep you informed, but it will take till after christmas.

12/23/2006, 01:28 AM
A floating hydrometer is actually extremely accurate. But, you have to calibrate it in a liquid of known specific gravity so that you know how far off the reading is and then you just add or subtract that amount from your reading.

12/23/2006, 07:24 AM
I remembered seeing a site describing how to prepare a solution having SG identical to seawater's. Fill the solution in the hydrometer and mark the division that the arm is pointing and you got a working hydrometer. And that's what I did, I think mine is 1.025 while it is pointing at 1.023. Sorry I can't remember the site.

12/23/2006, 08:00 AM
I've heard a lot of debate hydrometer VS. reftactometer and lately a lot of people have been saying the hydrometers are much more accurate.

I would love to know where to get some salinity solution (or make some) to calibrate.

12/23/2006, 10:38 AM
A glass hydrometer reasonable quality is by far the most accurate other than a lab grade refract. And the lab grade has to be calibrated to be as accurate. We are going for big round numbers and the additional abilities of a 1k refract mean nothing in anything other than research.

12/23/2006, 10:40 AM
Calibrate a hydrometer? Mine is sealed, how can you calibrate it?

12/23/2006, 10:41 AM
I have two swing arms (one from 1988) and they are not off by more than 0.003. Nothing lethal.

12/23/2006, 10:51 AM
<a href=showthread.php?s=&postid=8814794#post8814794 target=_blank>Originally posted</a> by Cuby2k
Calibrate a hydrometer? Mine is sealed, how can you calibrate it?

You need to float the hydrometer in a solution of known salinity eg. 1.025. If your hydrometer reads 1.024 then you know that each time you read you have to add 0.001 to your reading

12/23/2006, 11:14 AM
Wouldn't the calibration be set at the factory? I mean if they are going to mark the tube they need to have a reference point of where to place the levels.

EDIT: From tropic Marin website: These hydrometers never need calibration. Indispensable for scientists and the committed hobbyist. The higher price will soon pay off by an always exact salinity in the aquarium.

I have contacted Tropic Marin for some clarification regarding this issue and hope to hear from them soon. Since they are a German company I doubt they will respond before the new year but I will post response here ASAP.

12/23/2006, 03:39 PM
You can get a standard 35ppt salinity solution from http://www.vernier.com/

12/23/2006, 08:57 PM
This may already be well known information but a swing arm type hydrometer need to be kept clean and free of deposits to get good readings. I soak mine in vinager. I found that my hydrometer was reading much lower than actual after I cleaned it the first time.

12/27/2006, 09:56 AM
I got a reply from Tropic-Marin regarding the calibration of their hydrometers, his repy:

Thank you for your e-mail.

Yes, it is right that each Tropic Marin hydrometer is calibrated individually. You can recognize it by individual differences of the placing of the scale.

Kind regards

Hans-Werner Balling

Dr. Biener GmbH
Steinaeckerstr. 3-5
36367 Wartenberg

So from what I can see the hydrometer is still the most accurate method of checking SG as long as it is read and calibrated correctly. Once calibrated the sealed unit does not change reading.

12/27/2006, 10:07 AM
Yes, thats true

12/27/2006, 10:14 AM
I would use a hand calibrated float hydrometer over a swing type or a highend rafractometer any day of the week! I work in the precision optics industry and we manufacture the prizm's used in refractometers. they are made with tolerences of +/- .001mm. We use a Float type hydrometer to calibrate them once assembled. QC them checks them the same way with two floats.

12/27/2006, 02:31 PM
<a href=showthread.php?s=&postid=8812968#post8812968 target=_blank>Originally posted</a> by nick18tjetta
(That was back when you could perform a search on Reefcentral)

you still can, just pony up the yearly fee, or wait til after 11pm :p

12/27/2006, 02:37 PM
Does anyone have feedback on JBJ Digi-Lab TSS - Lab Grade Digital Temperature, Salinity, Specific Gravity Meter?



12/27/2006, 02:40 PM
whey you use a swing arm hydrometer you have to make ABSOLUTELY SURE there are no micro bubbles on the swing arm and then the meter will be real accurate! I use a small stick or something i can knock off the bubbles with and then i read the meter. If i don't do this the meter will definately be inaccurate. I have checked 2 hydro meters and found them to be accurate comparing to a refractometer as a reference. I'm sure if you go back and use your old hydrometer and knock off any bubbles on the swing arm, it will be accurate!

12/28/2006, 10:36 AM
<a href=showthread.php?s=&postid=8836164#post8836164 target=_blank>Originally posted</a> by dippin61
you still can, just pony up the yearly fee, or wait til after 11pm :p

Even non premium menbers can search any time of the day. Just use the search tools on the sidebar on the home page.

12/28/2006, 10:55 AM
<a href=showthread.php?s=&postid=8841986#post8841986 target=_blank>Originally posted</a> by michaeldaly
Even non premium menbers can search any time of the day. Just use the search tools on the sidebar on the home page.

that dont always work either. what i do is an advanced search on google and search by domain then just search reefcentral

12/28/2006, 11:09 AM
Originally posted</a> by pfish
You can get a standard 35ppt salinity solution from http://www.vernier.com/

I can't find it on there can you post a link right to it?