Hydrometer vs Refractometer

[fragNplug]

After reading this i guess its time to get one myself, im scared at what mine really is now.

[Johnny Reefer]

I have both, but haven't used the hydrometer in about 3 years. I always use the refractometer and will continue to do so. But a question comes to mind....if the error of a hydrometer is known, could the hydrometer not still be used and just simply apply the error in calculating the true reading?...or is an error in a hydrometer prone to fluctuate? (This is assuming the instrument is cleaned thoroughly after each use).

Cheers,

[Red Coral Aquariums]

A refractometer is possibly the most important initial piece of testing equipment you can purchase.
We have sold many hydrometers but always recommend the refractometer.

I have found that only approx. 5% of new hydrometers are accurate but once you find out how much they are off they (under proper usage) remain consistent. We test hydrometers going out of our store and they are an average of .04 out but have had numbers of .1.

Kevin

[midgetwaiter]

Originally Posted by mike31154

m..waiter, I'm not sure I fully understand your response to my quote? What is 'quite common' and how do you end up with 'the refractometer reading about 1.030...?? Bets on what exactly?

Erm sorry I was tired when I wrote that. 1) Yes I have found several refracometers that have buggered up when calibrated with RO/DI. 2) More often than not this nature of this mis-calibration has resulted in the refractometer reading 1.026 as 1.030 or there abouts. 3) I have bet 3 people that the problems they were having were the result of an incorrect salinity measurement by their blindly trusted refractometer and have won every time.

Originally Posted by StirCrazy

I read that and he said it is a good standard for initial calabration, but recomends that you check it once and a while against a sea water standard to make sure there were no manufacturing errors.

So basicly if you are using a good, refractometer the pure water is the way to calabrate it. It works for the labs and it will work for us.

If you have a questionable one then check it to make sure it is accurate at your SG

STEVE

Doesn't "questionable" perfectly describe the situation the original poster finds himself in? He has no way to determine if his refractometer is actually working correctly other than calibrating it with RO. Automatically assuming that the refractometer is correct because "hydrometers are bad" is not sound reasoning.