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Refractometer Calibration


andy
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I just mixed up a batch of Randy Holmes-Farley's 35ppt refractometer calibration fluid. It's a good thing I did, my refractometer was measuring high by a couple of ppt. I'll bring some of it to the next meeting at Mike's house, so if you want to calibrate your refractometer bring it to the meeting.

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Also, be careful when using commercial SG reference solutions. Some may be for use with electronic SG meters, so may conduct electricity like 35ppt seawater but not refract light like 35ppt seawater. Using a solution like this can give an incorrect calibration in a refractometer.

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I bought and tested the solution for my Marine depot meter...Andy I think you were there at Sea Horse that day shooting coral center folds! I didn't even know I was having a salinity problem until my new purchased Frog Spawn wouldn't open....water tested at 1.016 and meter read 1.024....We tested the purchased solution and it tested 5 points low ...needless to say I dumped the water out and recalibrated to Sea Horse's water ...and its now working perfect. I still check it once a week to ensure its holding it calibration.

 

Andy brought up a good point regarding what levels to test at....some say RO water to 0 is good .....some say you should have salt content in your water to properly test it ....but Andy mentioned that its accuracy could be restriced to a certain parameter within the scale.....1.020 -1.030 for example...and if you test to 0..then it would be off at the higher levels!!

 

Me personally.....I felt it was better to calibrate it at the level I wanted it to test at....so I used the water from tank that I knew was good.....and set it to that.

 

Thats what I get for not paying attention in biology!!!

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I bought and tested the solution for my Marine depot meter...Andy I think you were there at Sea Horse that day shooting coral center folds! I didn't even know I was having a salinity problem until my new purchased Frog Spawn wouldn't open....water tested at 1.016 and meter read 1.024....We tested the purchased solution and it tested 5 points low ...needless to say I dumped the water out and recalibrated to Sea Horse's water ...and its now working perfect. I still check it once a week to ensure its holding it calibration.

 

Andy brought up a good point regarding what levels to test at....some say RO water to 0 is good .....some say you should have salt content in your water to properly test it ....but Andy mentioned that its accuracy could be restriced to a certain parameter within the scale.....1.020 -1.030 for example...and if you test to 0..then it would be off at the higher levels!!

 

Me personally.....I felt it was better to calibrate it at the level I wanted it to test at....so I used the water from tank that I knew was good.....and set it to that.

 

Thats what I get for not paying attention in biology!!!

 

Mine worked the opposite way. I was reading at 1.024 and went to a friends house to see if his was working right. His was reading low compared to mine so we had his tested since we were heading to the store anyway. His was off but only by .003, which meant mine was actually off by .006:eek:. So I got the refractometer. Basically my tank had been at 1.032 for months. Everything has been fat, dumb and happy though so I had no clue. I am slowly dragging it back down now.

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Impur...Thats the fluid I bought and it was testing 30 ppm not 35ppm as i was informed. When i bought it I tested it at 77 degrees and I had to call Marine Depot for the conversion from 53mS. They said I should calibrate the meter to 35 pm with the fluid. I did...ran a few weeks and added my first coral, Frog spawn ....it never opened and I went to Sea Horse and Issiac tested the salinity and it was at 1.016 !! I returned home and tested the water again with the meter...1.024. I recalibrated the meter with the same fluid again at .35 @ 77 degrees.....tested the water and again 1.024....took the calibration fluid to Sea Horse and tested the actual fluid.....30 ppm.

 

I called Marine Depot and was told that the fluid I purchased is for the " Pin Point Salinity MONITER and not the meter....but thats what they sell to everyone ....and I must have gotten a bad batch! ! I guess %&@* happens.

 

I would recomend everyone to test their meters monthly....and test it against a known....and set it to a salinity level close to what our purposes are 1.023 - 1.026 if setting it to zero RO water ......it very well could be off +/- 5 at the higher scales .....but hey...if your fish / corals are happy.... why change. They all adjust a certain amount. IMO

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Trever, Darrellw and I have all calibrated our refractometers to the 35ppt sample. Both Darrellw and I were reading ~3 ppt high, while Trever was right on. Darrellw and Trever had recently calibrated to zero with RO/DI. I hadn't calibrated in years.

 

Interestingly, Darrellw and I have the same (or extremely similar) refractometers... light-ish blue with brushed aluminum fittings. Trever's is darker blue with polished chrome fittings. Trever's is also noticeably heavier.

 

It's really too small a sample size to say anything for sure, buuuuuuutt... if you have a light-ish blue with brushed aluminum refractometer that's calibrated to zero you might want to check it against a 35ppt sample.

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No problem! It was an eye-opener for me. I slammed my salinity right back up (I don't recommend it under normal circumstances) because my trachy and one acan were on the way out. The trachy looks way better now, the acan was pretty far gone.. I think one polyp may make it. Duncan and chalice frag look happier now, too.

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I'm not going to be able to make the meeting after all -- I've got a wall to build in the basement and don't have much time to do it so every weekend day is pretty much spoken for :(

 

Dennis, can I swing by your place some evening this week? I can drop off the solution (maybe you can bring it to the meeting?) and we can take some pics of your tanks. LMK.

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