Two Hydrometers - Two Specific Gravities

[NanoMark]

Hello.

I am getting two values for specific gravity from two hydrometers and I don't know which to believe:

 

Instant Ocean Hydrometer: 1.027

 

Coralife Deep Six Hydrometer: 1.023

 

Has anyone experienced this before? Which one tends to be more accurate?

 

Mark

[ezcompany]

people will tell you to get a refractometer

[mooman]

From what I understand, all hydrometers are inaccurate to some degree. Luckily they are usually copnsistantly inaccurate, meaning once you calibarate it it should work fine. Find a LFS that has a refractometer. Take your hydrometers in and test them in one of their tanks. Have them test the same tank with the refractometer and then use a sharpie to write (+) #.### or (-)#.### on the back of the hydrometer, then just add or subtract this value from whatever reading you are getting.

 

Ohh, just remembered hearing from a guy that I worked with that over time hard water deposits can build up on the arms of hydrometers and affect the reading. Soaking it in a viniger and water solution before calibration and periodically might be worth it.

[NanoMark]

ok thanks guys.

 

I'm a chemistry major so I think I'd like to invest in a refractometer. What do you recommend?

[formerly icyuodd/icyoud2]

actually thats not true. salt build up and other crud on the needle/swing arm can effect the accuracy of the hydrometer. very small amounts of crude in the pivot points can cause friction and render the hydrometer useless.

i checked mine against a refracto every couple of months. i bought my refractometer

the day i found out my hydrometer was screwy.

my reef was at 1.30 and who knows for how long.

[brent-konieczny]

Always reference the hydrometer by subtracting some from the value you get. In just about every case using a hydrometer will cause you to make your salinity higher than desired. This is because the crud on the arm and inside that keeps it from floating up to the right reading. That means that if your hydrometer says 1.025, the actual level is higher. To be safe I use my hydrometer to read 1.023-1.024, which means the actual salinity could be between 1.023-1.026, but not higher (in the harmful range).

 

Wow! I wonder if anyone else will understand what I just wrote.

[mooman]

Sorry, what part of what i said wasn't true?

 

Calibrate it against a refractometer

Clean the crud off with vinigar and water before and periodically after you calibrate it.

 

Just asking since I'm a bit of a newbie myself.

[icenine]

Don't forget how temp effects a reading as well.

 

...and yes, go get yourself a refractometer with automatic temperature compensation. If all the correction and compensation malarkey in the posts above don't convice you, what will? (always subtract?? consistantly inaccurate?? lol, gimme a break) ....or maybe you would get better readings by standing on your head while facing the north pole.

 

Decent refractometers can be had for as little as 30 bucks.

[The Keeper]

Being a newbie to reefing, ive been keeping my tank at 1.025 for the past 4 months using an instant ocean hydrometer.

 

This week my digital sality and sg guage that I got from Vermont Reef's groupbuy should arrive. When that happens I will be running some tests on 3 different hydrometers, 2 different refractometers, and the floaty type ones as well. I will also be seeing how much effect you get by cleaning the hydro with vinegar before using it. I have two IO ones, one that gets dunked in the tank and then left alone, the other gets cleaned with fresh water after every use. I'm going to write down all my results and present them in this thread.. or maybe start another..

[formerly icyuodd/icyoud2]

Sorry, what part of what i said wasn't true?

 

Calibrate it against a refractometer

Clean the crud off with vinigar and water before and periodically after you calibrate it.

 

Just asking since I'm a bit of a newbie myself.

 

the consistantly inaccurate part