Refractometer Calibration

Well I had a friend who is a lab tech { hobbyist} for a sate lab to show me yrs ago that If I checked S/g using a refractometer I should allow all fluids to get to a room tempature 70 degs F and then use some distilled water to adjust to zero then use Witch Hazel and to double check the set/calibration of the unit . Using the witch hazle last to double check the distilled water the unit should read 43 ppt then that will or would equal at 1.030 that. Its fast simple and very accurate. And uses all common household products setting most peoples medicine cabinets . Well the witch Hazel anyways :>) the distilled water is another matter.
But all the fluids used to be tested for the calibration should be the same temp as the refractometer. And who's to say the room ambient temp and the fluids temp or the meters are perfectly adjusted in temperature ? It could cause slight distortion in the readings for calibration . Close is good I would think. I doubt a ocean has a constant S/P gravity reading 24/7 365 , In-fact as most tropical reefs are closer to land then I'd assume that rain run off would cause more fluctuation around them then from further out in the open ocean ? But that just me using common sense again got no data.. But I'm sure someone does Also uing this methoed last time I checked a refractometer I like to run mine near 30 ppt or 1.024 1.025 + or - a little

 

Randy's article is out now.

Refractometers and Salinity Measurement by Randy Holmes-Farley - Reefkeeping.com

 

I just got one of these delivered to the house today in hopes to make things easier. After reading this I think I just made it harder. Guess I had better get some sleep tonight and read the rest of the article before I calibrate mine and use it.

 

this has helped my out a ton! So i should just calibrate my refractometer to 1.028 with the solution, so that its actually 1.0265 that im targeting? Is this right?

 

No, if you are using the calibration fluid (35ppt/53ms) you calibrate for 1.0265 when using an NaCl refract..
However, with an NaCl refract, if you are doing hyposalinity treatment, your reading will be more accurate at 1.009 if you calibrate with water for a 0 reading.
Something that many people have failed to make note of is the fact that their Na Cl refractometers will only be out by .0017 when calibrated with water to 0, but Randy/Boomer find them off up to .003.

Now, some hobbyists have purchased NSW refractometers and assume that they can STILL calibrate with water, setting for 0.
Based on the tests, it is not inconceivable that the NSW refractometers are also some times defective, giving errors like the NaCl refractometers minus the calibration error.

 

So a NaCl calibrated to 35ppt fluid will read 1.026 when tankwater IS 1.026 (within manufacture's limits) Moral of the Story: get calibration fluid?

 

Yup. For $5-6 you'll have a lifetime supply (almost) and good peace of mind.

 

I had already ordered some up earlier due to 0 ptt ro/di calibration error but until reading this thread I never kenw WHY! Thanks again Inwall! (And Sacul)

 

Yup I always use the 35ppt fluid. It was cheap and the one bottle I bought is still almost full a year later. I think it will last for the life of my refracto. Just buy the fluid and have piece of mind.

 

I dont know what model i have (got it from Drs. Foster Smith years ago) but when I calibrate with RO/DI water it is no where close to when I calibrate with a 35 ppt known solution.