Salinity,salinity salinity

[OoooDRAGONoooo]

Hi all,if my deep six hydrometer reads 1.023and my refractometer ,(both new) reads 1.031. Which one is likely to be closer to truth.(I have calibrated using rodi water.i know it's not perfect procedure,but the two figures are too far apart.help.please

 

[CodeBlueMedic]

If your refractometer was calibrated per the instructions (mine called for distilled water), then it is the most accurate. Hydrometer's (mine included) are infamously inaccurate

 

[shesacharmer]

My hydro is terrible...a piece of trash. My refractometer was calibrated with distilled water also per the instructions and I have not had a problem relying on it.

 

[thegrun]

I would certainly invest a few dollars and get some 35ppt calibration fluid and be sure. Even though your refractometer instructions tell you to use ro/di water for calibration, at the salinity levels we measure at the refractometer could be off by several points if you use ro/di water. A single point calibration instrument should always be calibrated with a solution as close as possible to the anticipated reading level as possible.

 

[downbeach]

+1 On the calibration solution. You should be using a solution that is at the same refractive index as the sample you'll be testing. Here's a good article:

http://reefkeeping.com/issues/2006-12/rhf/index.php#13

 

[disc1]

If you calibrated with RODI then it depends on the exact type of refrac you have and there is no way to know which of those numbers is accurate if any of them are.

 

[OoooDRAGONoooo]

Yay for replies.cant buy calibration fluid it seems unless I get it posted from the U.S.my tank will hopefully be cycled soon,I will test the salinity with fish and coral

 

[disc1]

You can make a DIY calibration fluid that will match seawater in refractive index, but note that it is ONLY good for refractometers. 3.65g of table salt in 96.35g of DI water will give you a solution that is 36.5ppt in sodium chloride and will match right up to 35ppt seawater on your refrac. There are similar recipes for hydrometers and conductivity meters but the refrac one is the only one i remember off the top of my head as I make that one all the time.

 

[OoooDRAGONoooo]

Ty very much.