Salinity Help

[rjjr1963]

I just started my QT tank and I have a hydrometer and a refractor. They don't read the same value.

Coral Life Deep Six hydrometer = 1.026.

Refracter + 1.022


I've calibrated the refractor and it's right on the money.

How do I know which one is right?

 

[cloak]

Assuming you used both instruments correctly, probably the refractometer. You might want to run a couple more tests with the swing arm hydrometer though. This time let the thing sit for about 5 minutes and nudge the needle with a stick a few times to remove any micro bubbles that may be attached to it.

 

[TimeConsumer]

Did you calibrate the refractometer with a reference solution or with RODI? Because the latter is not very accurate.

 

[Fish Keeper82]

Did you calibrate the refractometer with a reference solution or with RODI? Because the latter is not very accurate.

Agreed
This article expains why its off using RODI
http://reefkeeping.com/issues/2006-12/rhf/

 

[Auston]

Don't bother with swing arm. If your worried about calibration you could always bring a sample to your lfs and have them double check

 

[rjjr1963]

Did you calibrate the refractometer with a reference solution or with RODI? Because the latter is not very accurate.

I used the reference solution. After my first post I found a few small bubbles on the arm of the hydrometer and after I got them off my reading is off by .001 so not as bad as I thought.

 

[Auston]

Agreed
This article expains why its off using RODI
http://reefkeeping.com/issues/2006-12/rhf/

The article says rodi water can be used...

 

[Fish Keeper82]

The article says rodi water can be used...

Scroll down to the Imperfect Refractimeter Calibration: Slope miscalibration section and the following section.

It explains how the refractometers we use are for brine water not seawater. So calibration with solution will be more accurate.
I didnt say you couldnt use RODI just that known calibration solution will yied more accurate results. My refractometer is off .003 with RODI water.