Go figure, Refractometer was off.

BTW when said hydrometer I was referring to a floating hydrometer not a swing needle. Therefore air bubbles and rinsing should not be factors of error. Temperature is but that can be corrected for using several calculation methods. Calibration error is the main concern that I can see which would be dependent on the quality of your hydrometer. Any thoughts?

 

So if you recheck with a hyrdrometer are you going to adjust the water accordingly? If not, why recheck in the first place. And if so, there is no need for a refractometer, and you're limited yourself to an instrument with a lower precision.

 

Bulk Reef Supply will give you a free bottle of calibration fluid if you buy a refractometer from them.

 

As for rechecking you might accept a 5% discrepancy or maybe 10%. If there is you would probably assume that the refractometer needs to be calibrated because a floating hydrometer, if calibrated correctly at the factory, should never need re-calibration, only a temperature adjustment. As far as precision I think you're referring to resolution. A floating hydrometer will typically have a resolution of 3 decimal places depending on the quality. I don't know how fine the resolution is on a refractometer but once you exceed 3 decimals you're results may no longer be relevant because a specific gravity variation of 0.0001 could be insignificant. Furthermore the question is not which is more accurate, assuming correct calibration they should both be equally accurate, but which is more precise, ie. which is more susceptible to systematic error.

 

I have to agree about the hydrometer. I use one. It is like anything else you use to test things with... If you don't use it property or know the correct method scientificly then you will get wrong results. If you actually know what you're doing and you take proper care of your equipment you will get acceptable readings from my experience. I've been pretty dead on with a calibrated refractometer using my hydrometer.

 

Ah, a floating hydrometer is a different story. That's something I would use to check a refractometer against.

A swing arm hydrometer makes a nice door stop.

 

I agree that swing needle hydrometers are too error prone to e relied upon. So the next question is why should I spend more on a refractometer when I can use a floating hydrometer which is
1. Cheaper
2. Easier - does not require calibration
3. Sufficiently accurate and having sufficient resolution
Same goes with electronic salinity measurement

 

Dont you need to read a floating one from the side? If so that would be difficult in my 5 gallon bucket I make my water in.

 

It sure would. In fact I don't think you could get an accurate reading in anything but a cylinder of fluid as per the directions for proper hydrometer use. I use a graduated cylinder.

 

BRS sells theres that way. I just got one and it had a pretty big bottle of calibration fluid with it $35 i think. How often do you guys recalibrate?