Myka
Valuable Member
I did some testing this week, this is what I got. I'm using an old ATC refractometer (prob 20 years). The scale looks like the VeeGee one. It's a great refractometer and keeps its calibration well.
I carefully measured out salt and water using a 100g digital scale and made calibration solution according to Randy. I made it three times. I made it very carefully twice, then once I was a bit sloppy about the measuring so I could compare to see how sensitive the solution is to changes. The sloppy one was off from the other two by 1 ppt. The two carefully measured out were exactly the same. http://reefkeeping.com/issues/2006-12/rhf/#18
All calibration solutions were allowed to sit on the refractometer for 45-60 seconds for ATC.
So I first washed the refractometer with a mild soap solution, dried it, and let it sit for 5 mins to be room temperature. Then I calibrated with Randy's solution. After calibration I re-checked the solution and found it to read exactly 35 ppt.
I measured a freshly opened bottle of TLF AccuraSea Seawater Reference Calibration Solution. It read 36 ppt.
I measured a freshly opened bottle of Sybon Standard Seawater 35 ppt Calibration Solution. It read 32.5 ppt.
I measured a bottle of TLF that had been open for awhile, used a couple dozen times, carefully closed every time. I do not like the big opening on this bottle! So much room for contamination and evaporation! This bottle read 37 ppt.
I measured a bottle of Sybon that had been open for about 2 years, about 1/2 full still. It read 31.5 ppt.
I measured an old bottle of Sybon that had been open for probably 6 years. It only had maybe 1/4" of solution left in it. It read 31 ppt.
Interestingly, I had a Triton test done last year in August. I was using the Sybon above that is listed as about 2 years old (reading 31.5 ppt), and using Jim's spreadsheet to determine salinity from Triton results, my result was 32 ppt. Although this anecdotal evidence has a big time gap, the three Sybon solutions read only 1.5 ppt difference from brand new to 6 years old, so I would think the solution would not change much in the last year.
All these points lead me to believe that Sybon is inherently low. I didn't think I believed the TLF solution when I first tried it out a few months back and found it to read so much higher than the Sybon which I had relied on for so many years. Then I remembered the Triton test results indicating low salinity. Then Randy's solution is very close to the TLF also.
So now what I do is use the new Sybon (because I like the bottle better), but I calibrate it at 32.5 ppt rather than 35 ppt. Since it is a seawater solution, I should get an accurate calibration. After testing, this does seem to be the case. I am confident that salinity in my tank now is at the very least, closer to 35 ppt than it was.
I carefully measured out salt and water using a 100g digital scale and made calibration solution according to Randy. I made it three times. I made it very carefully twice, then once I was a bit sloppy about the measuring so I could compare to see how sensitive the solution is to changes. The sloppy one was off from the other two by 1 ppt. The two carefully measured out were exactly the same. http://reefkeeping.com/issues/2006-12/rhf/#18
All calibration solutions were allowed to sit on the refractometer for 45-60 seconds for ATC.
So I first washed the refractometer with a mild soap solution, dried it, and let it sit for 5 mins to be room temperature. Then I calibrated with Randy's solution. After calibration I re-checked the solution and found it to read exactly 35 ppt.
I measured a freshly opened bottle of TLF AccuraSea Seawater Reference Calibration Solution. It read 36 ppt.
I measured a freshly opened bottle of Sybon Standard Seawater 35 ppt Calibration Solution. It read 32.5 ppt.
I measured a bottle of TLF that had been open for awhile, used a couple dozen times, carefully closed every time. I do not like the big opening on this bottle! So much room for contamination and evaporation! This bottle read 37 ppt.
I measured a bottle of Sybon that had been open for about 2 years, about 1/2 full still. It read 31.5 ppt.
I measured an old bottle of Sybon that had been open for probably 6 years. It only had maybe 1/4" of solution left in it. It read 31 ppt.
Interestingly, I had a Triton test done last year in August. I was using the Sybon above that is listed as about 2 years old (reading 31.5 ppt), and using Jim's spreadsheet to determine salinity from Triton results, my result was 32 ppt. Although this anecdotal evidence has a big time gap, the three Sybon solutions read only 1.5 ppt difference from brand new to 6 years old, so I would think the solution would not change much in the last year.
All these points lead me to believe that Sybon is inherently low. I didn't think I believed the TLF solution when I first tried it out a few months back and found it to read so much higher than the Sybon which I had relied on for so many years. Then I remembered the Triton test results indicating low salinity. Then Randy's solution is very close to the TLF also.
So now what I do is use the new Sybon (because I like the bottle better), but I calibrate it at 32.5 ppt rather than 35 ppt. Since it is a seawater solution, I should get an accurate calibration. After testing, this does seem to be the case. I am confident that salinity in my tank now is at the very least, closer to 35 ppt than it was.
