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Old 02-08-2004, 07:44 PM   #1
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measuring specific gravity

I just purchased Marine Environments SG tester to double check my Coralife Deep Six SG tester. I am perturbed. The Coralife reads 1.023 while at the same point in the tank the Marine reads 1.019 that is a big difference No? Short of buying a refractometer what should I do?
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Old 02-08-2004, 07:53 PM   #2
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I think that is a pretty big difference. Did you make sure you soaked the DeepSix in water prior to use as per the instructions? Also, did you make sure that they were no bubbles stuck to the swing needle.

FYI, I used a Deep six for a few months before I broke down and purchased a Refractometer on eBay for around $40. I was suprised to see, though, that my DeepSix was fairly accurate. In fact, it was only off .005 SG's from my refractometer.
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Old 02-08-2004, 10:47 PM   #3
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Did you calibrate the salinity tester?
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Old 02-08-2004, 11:09 PM   #4
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Yes I washed it and soaked it in vinegar to remove any deposits. I am positive that there were no bubbles, and took about 6 different readings on each and they were all consistent. As per reefrunners post how can you calibrate, what is your reference point?
I will look around some more for a reasonable priced refratometer.
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Old 02-08-2004, 11:16 PM   #5
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I will look around some more for a reasonable priced refratometer.
PremiumAquatics is selling the RHS 10ATC for around 40 bucks right now, or at least they were a few days ago Excellent refractometer and they are one of our sponsors and that is a heck of a price

You may not, but I would think it was necessary, try testing RO/DI water or distilled, it should have a SG of 1.0 and a salinity of 0ppt. You might also check to see if it is temperature dependant.
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Old 02-08-2004, 11:17 PM   #6
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To my knowledge there is no way to calibrate a DeepSix. I have no idea about the Marine Environment's tester.

In the end, a refractometer is the best choice. They are so simple to use and are highly accurate. It kinda like the difference between a pH reagent kit and a digital pH tester. Once you use the digital tester, you will never look back.
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Old 02-08-2004, 11:19 PM   #7
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Premium Blue Refractometer - RHS-10ATC
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Code: REFRACT-PA
Price: $42.95
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Old 02-09-2004, 05:59 AM   #8
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I wonder if a simple hydrometer would not be suitable once it is calibrated. The problem with them seems to be not that they are inaccurate, but that they may not have the internal paper scale placed properly. If you check it in a tank of known specific gravity to detect any error in placement of the scale, it ought to work fine.

Am I missing something?
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Old 02-09-2004, 09:20 AM   #9
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I wonder if a simple hydrometer would not be suitable once it is calibrated.
Sure it would, it still won't be as accurate as a refractometer, but certainly accurate enough for a reef tank. The thing is, a refractometer is just as easy to use and if you have it to verify the accuracy....then you may as well use it on the tank. If your talking about the floating hydromters, they are either very accurate or very inaccurate. With some of the shorter ones (less that 12" in length) I don't think it will matter. The swing arm hydrometers should be rinsed with RO water after every use and soaked in vinegar once per month to remove any mineral deposits on the hydrometer.
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Old 02-09-2004, 11:33 AM   #10
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I used the Deep Six for the first month of my reef and then took a sample to my LFS, boy was I shocked. The Deep six read 1.023 and the LFS refractometer read 1.027! I nearly upped my salinity to 1.030 because the Deep Six was way off. I quickly went out and eBayed a Refractometer and now all is great. Between the digital pH pen and the refractometer my parameters are so easy to read and my confidence is highly stabilized.
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