How off is your hydrometer!

[zerocool5878]

I have been maintaining

my nano reef at 1.023sg

75 gal FO 1.019

And my sons pico fowlr at 1.019

all with a hydrometer. I have 2 of them and they always give the same reults. One of them is only 1 month old. I always rinse them after testing and boy are they off.

 

Today i bought a refractometer at my LFS. They were showing me how off these really are right in the store. They calibrated it and showed me how it works. I came home and tested all 3 of my tanks.

 

nano 1.026

75 FO 1.021

pico fowlR 1.021

 

Im really glad I bought this.

 

Cheers

[moe sizlack]

IIRC you have to use the hydrometer at the correct temperature.

[travisurfer]

i don't know, i use a refractometer

[Uhuru]

my IO hydrometer was off by about .002

 

if it's consistently off by the same amount you can still use it

[moe sizlack]

I'm still putting my money on the temp difference.

Expansion, contraction... all that science mumbo jumbo.

[justinl]

I know my FOWLR is sitting at 1.024 and i maintain that with my hydrometer that consistently reads 1.018. it works well enough even if i cant shoot for a diff SG.

[Darklyte24]

mine reads 1.022 so i added more salt came out to 1.023ish, had a guy measure it with refractometer ? or was it chemical, he said it was a bit high, 1.026 so he said my meter was off by 4...

 

oh ya mine is the deep 6 by coralife

 

oh ya again, i heard you should measure at 80*F?..

[zerocool5878]

IIRC you have to use the hydrometer at the correct temperature.

 

 

I believe that to be incorrect. the two that I have are Seatest and instant ocean swing arm hyrometers. These are no supposed to require temp correction.

 

However they do suck at measuring sg.

 

I don't think that the standard corrections would apply to these 2 hydrometers.

[Darklyte24]

http://www.thatpetplace.com/pet/product/ad...e=10#resultBody

 

 

one of them says 77*F

[Travis]

surprisingly, mine was off by -0.001....I could have saved some cash and got a new frag...

[zerocool5878]

Just found this

http://www.reefkeeping.com/issues/2004-07/rhf/index.php

 

To back up my beliefs that some swing arms do not need temp correction. You can see that the ones listed in the above link show the same results from 68-85 degrees. So temp correction surly will not work on these brands.

 

SeaTest, Deep Six, Instant Ocean and eSHa Marinomat

[HecticDialectics]

A few degree temperature difference won't matter... it'll read the same.

[Gvtv44]

.002

Although temp DOES matter, due to thermal expansion, which affects density (Specific Gravity) but the effect is so miniscule, it doesn't matter for our purposes.

Volume after Expansion= (Coefficient of expansion)(Volume original)( Delta T)

So if you have a given volume of say, 100, and the hydrometer is meant to read at 75 and your tank is 81, then the percent error is... .126%... so the hydrometer would read roughly 1.026 instead of 1.025. But Hydrometers are so inaccurate due to other reasons (miss manufacturing, bubbles, etc) temp differences are negligable.

[BibleSue]

Mine is off-off on a shelf FOREVER!!!! Refracto all the way! What a sweet piece of equipment!!!

[Fishfreak218]

I got rid of mine a LONG time ago