Hydrometer vs Refractometer

[Fermat]

I have heard from several reef keepers now that hydrometers are useless.

I have a hydrometer, and it seems very consistant. If I do multiple tests, it always reads exactly the same, and if I add salt to the mix it reads a higher value as expected. The manufacturer claims it is accurate to sg of 0.001. In reading up on refractometers, they also claim an accuracy of 0.001, exactly the same as the hydrometer.

Are refractometers better, and why?

 

[kau_cinta_ku]

mainly it is due to refractometers stay more constant over time than hydrometers. where as hydrometers if not taken well cared of, the swing arm will stick giving you a false reading, bubbles on the arm will give you a false reading, ect. but a new hydrometer works well it is just that over time without proper care they will not be as accurate

 

[smcnally]

I thin kthe accuracy claims on the hydrometers are false. I know too many people (including myself) that had hydrometers that were way off. Mine was off by .003 and I've seen some even worse. The biggest benifit of a refractometer is that if is is off, you can calibrate it. Also, there is such a little amount of water used, it takes no time at all for it to get to room temperature, so all your readings are the same.

 

[Dubbin1]

<a href=showthread.php?s=&postid=8522909#post8522909 target=_blank>Originally posted</a> by kau_cinta_ku
a new hydrometer works well

Then explain to me why I had 3 NEW hydros and got 3 different readings. Thats the day I got my refractometer and found out that all three of those new hydros were wrong wrong wrong. As much as we spend in this hobby the price of a decent refractometer is nothing.

 

[wiszmaster]

funny .. i just started the same thread in a local section of RC:
http://reefcentral.com/forums/showthread.php?s=&threadid=970055

COPY&PASTE

Hydrometer Vs. Refractometer
I took some water samples of the tank, the tap, and the RO/Di down to boardroom yesterday .... to make sure the whole house RO was doing OK, and to make sure the RO/DI for the tank was doing its job as well .. everything checked out just fine.

Then while testing the tanks water the calcium was in the 150-200 range .. awefully low. tested the salinity .. and it showed as 1.019-1.020 ...

NICE! my hydrometer read 1.026 all day long on the same water.

OK - maybe error on rich's side.... i went home, unpacked my refractometer that arived by FedEx today ... tank water = 1.019


I've been bring the water up over the past 6 hours ... its now @ 1.026, and should probably not change ... maybe 1.025 .. the refugium still read @ 1.024 while tank & sump were @ 1.026



there are alot of refractometers on ebay for pretty cheap .. how good & acurate are they ? no idea.... but i've seen some up there for mid $20's to low $30's ....



ryan ... i know when i was down last time you mentioned that my calcium was a bit low as well, and we spoke about the salinity ... @ that point my hydrometer read 1.023 & i brought it up to 1.026 .. or so i thought ...according to it. i was probably @ about 1.015-1.017 back then ...

could that have been the reason for the tanks cloudyness, a die0off due to the low salinity level when i added the extra 90 gallons on sunday after installing the sump/fuge

 

[wiszmaster]

short version of the story .. the HYDROMETER was .007 off ... that ALOT!
in the meantime my fish developed ich ....

 

[michaeldaly]

A hydrometer is always consistant(Im talking about the glass type) but you have to first place it in lighid with a known specific gravity to see how far off it is and then add or subtract the amount when you do a reading on your tank wanter.

If you can get hold of lab grade hydrometers they are also imensly accurate.

 

[wiszmaster]

the glass ones tend to be much more acurate, than the plastic ones ... glass being the tubes, not the ones you pill up with water.

Glass - good

http://www.williamsbrewing.com/LABORATORY_SPECIFIC_GRAVITY_P539C74.cfm

plastic - bad

http://www.drsfostersmith.com/Product/Prod_Display.cfm?pcatid=4952&N=2004+113761