specific gravity question

sldrdvm

sldrdvm

Member
Hey. I am new to the marine aquarium hobby and have a question. I have both a swing-arm Coralife deep six hydrometer and a temperature compensating refractometer. I have followed the exact directions for both (calibrated the refractometer at 68 degrees with distilled water and let the hydrometer sit overnight with saltwater). However, now when I test my water, the two instruments give me very different readings. (i.e., the hydrometer says 1.014 while the refractometer says 1.023) Which should I trust?
 
gmann1139

gmann1139

Active Member
What's scarier is that they're not only inaccurate, they're imprecise.
Meaning that if you take three readings, they will vary several ppt.
I see-sawed the salinity in my tank for a few weeks, trying to hit my target of 1.025, before I finally broke down and got a refractometer.
 
sldrdvm

sldrdvm

Member
Well, I am a veterinarian and use a refractometer at work almost every day to measure specific gravity of urine, and know that they are/can be very accurate instruments. I just can't believe the hydrometers could be so crappy. Why waste your money on a hydrometer if it isn't accurate?
 
maryg

maryg

Member
The swing arms are a joke. The floating glass ones are better, but a refractometer is the best. I finally got one.
 
sldrdvm

sldrdvm

Member
Thanks guys for making me feel better and trust my instincts. I just wish I hadn't wasted money on the hydrometer. At least it wasn't much.
 
pezenfuego

pezenfuego

Active Member
Originally Posted by sldrdvm
http:///forum/post/2916970
Well, I am a veterinarian and use a refractometer at work almost every day to measure specific gravity of urine, and know that they are/can be very accurate instruments. I just can't believe the hydrometers could be so crappy. Why waste your money on a hydrometer if it isn't accurate?
Well, actually floating hydrometers (while usually not accurate) are pretty precise...so long as the temp of the water doesn't change too much. But agreed, refractometers triumph.
 
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