salinity question
 

i got my refractometer in the mail last week and tried it out today.
Big difference and i'm wondering if i calibrated correctly or if there really is that big a difference between the hydrometer and the refractometer.
Hydrometer reads 1.027, Refractometer reads 1.023.
I think i may take a sample to my LFS and get them to test and see. that seems like an huge difference!
has anyone else had this kind of experience?

Yeah I have a problem with my hydrometer, reading .003 + higher then it should, they arent reliable. So I'm in the market for a refractometer, I would take it to lfs for proper calibration, but other then that I'm sure your hydrometer is off

you can get calibration fluid, i would bet the refractometer is correct, my deep six hydrometer was out 4 points, it was reading 1.023 when actual was 1.027, my snails stopped dying after i corrected the salinity.

mine too lol. poor little buggers. haha, thats why I'm glad I know how much my hydrometer is out, and glad to know I'm getting a refractometer for xmas

RO water at the same tank temp should read zero on the refractometer, if it's not adjust it with the screw driver typically provided. They usually need to be calibrated as salinity is temperature dependent.

Um, don't you mean distilled water Steve?...... I wouldnt callibrate a refractometer with RO....but that's just me I guess:wink:

Wouldn't bother myself, if you want to go through that much trouble it's up to you but I put money on it not making a difference. Pretty much everyone has RO water on hand and realistically you're interested in the change of salinity from your source water and mixed saltwater plus if you're off by a tenth of a percent it won't mater, acceptable salinity is pretty big range, consistency is more important. My tank does just fine using a refractometer calibrated with RO.

well if you have an RO unit and are sure of the TDS, then maybe........but I wouldnt trust the store bought RO or the Culligan man for having a low TDS

BLANK

i took my water and refractometer in, got it calibrated...it was one point off and all is well.
my hydrometer was way off.

Not to get technical but your refractometer measures salinity in ppt (parts per thousand) so even if your RO water was way out at 35ppm (parts per million) you'd still only be out by 0.035 ppt on your refractometer. Accuracy on a scale measured by your eye is equal to +/- half a mark which in the case of all the refractometers I've seen is 1 ppt, so you're refractometer even if calibrated perfectly is technically only accurate by +/- 0.5ppt. I wouldn't worry about that extra 0.035ppm, you couldn't even tell the difference when you calibrate it. :rolleyes:

Some salinity tips from Randy Holmes-Farley: http://reefkeeping.com/issues/2006-12/rhf/index.php

Fwiw, my hydrometers are out by 0.007 and 0.008.

I use DI water, sometimes even tap water and have seen little to no difference when calibrating my refractometer at the 0 level and that's with 210 TDS tap water. It is of course possible that the 'slope' of your refractometer could be off making the 0 cal inaccurate at the salinity range you like to keep your system at. It most likely boils down to each individual refractometer. All I know is my critters are happy & I've never used calibration fluid to dial in my refractometer. I didn't pay enough for the thing to warrant using lab grade calibration fluid on it. I reckon as soon as you open the calibration fluid bottle or whatever it comes in, it's no longer useful for future use. If I was going to get that precise in calibrating my instrument, I wouldn't use the fluid more than once. I'm more concerned about ensuring my water change water is as close as possible to my system water since I tend to do fewer, larger water changes. This is where I value my refractometer, whether it's off .00? points or not, as long as both readings, make up water & system water are within .002 of each other, I'm good.