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Old 09-26-2009, 10:34 AM   #1
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swingarm hydro -vs- refractometer

I have a couple questions.

I started out w/ a swingarm style and recently purchased a refrac.
I'm pretty sure I calibrated it correctly.
My swingarm was giving readings around 1.021-1.023.
I measured w/ the refrac and got readings around 1.025.
I'm not sure of the refrac brand...model is RHC-10 ATC.
Is is possible to have that much variation between swingarm and refrac?

I have had a couple fish and a shrimp die off since starting the tank.
Could higher salinity have been a cause?
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Old 09-26-2009, 12:12 PM   #2
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Being anywhere in 1.022 to 1.026 I would think would be fine for your fish and shrimp, unless there were large swings there that could've caused problems.

I've never used a hydro, personally, as all my research showed refracs were much more accurate. I would suspect that what you're reading with the refrac is probably more realistic than what you're getting with the hydro. Plus, the readings are really close when you think about the scale we're measuring here.
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Old 09-26-2009, 01:27 PM   #3
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I had the same type jump when Iswitched. If is a temp correcting refrac, make sure you give the water sample a30 seconds to match the temp of the prisim. Also, I calibrate mine on a regular basis.
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Old 09-29-2009, 07:43 PM   #4
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How did you calibrate it?
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Old 09-29-2009, 07:45 PM   #5
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All the ones I have seen come with a way to calibrate. Mine has a very small screw to turn. I use my RO water as a based and adjust until it reads 0.
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Old 09-29-2009, 07:52 PM   #6
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Calibrating with RO or distilled water will not calibrate the refractometer precisely - I tried this myself and then took my refractometer to my LFS and tested it side by side with theirs with the same water sample and mine was off just a bit. They then calibrated mine using calibration fluid and it matched spot on.

You really need to buy the calibration fluid ... it has a constant specific gravity of 1.0264 to calibrate your refractometer. It's only $8.00 a bottle.
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Old 09-29-2009, 08:08 PM   #7
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You actually should use the pinpoint calibration fluid and not RO even though the directions said to use RO. I had my 1st refractometer go bad and If I had only followed the directions and used only RO for calibration I never would of caught it and probably could of killed my fish as I was adjusting the salinity (this is when it crapped out) for hypotherapy. I have Ccapt to thank for that excellent advice. Once you adjust the refractometer to the fluid @ 35 ppt you should be able to put RO on it afterward and it should be dead zero.(with my unit it went way below zero after the calibrating to 35 ppt, then I calibrating it with RO then put a sample of the calibration fluid and the results indicated a whopping 43 ppt. Something to think about.

Oh yeah, you think the difference between the swing arm and refract (to be expected) is wild, I took my water sample to 5 LFS's all of which are using the swing arm hydro and all five plus my hydro making it six different tests yielded six different results ranging from 1.019 to 1.031. Now that's mind blowing when you're trying to get it right.
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Old 09-29-2009, 08:15 PM   #8
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Quote:
Originally Posted by Boulder View Post
Calibrating with RO or distilled water will not calibrate the refractometer precisely - I tried this myself and then took my refractometer to my LFS and tested it side by side with theirs with the same water sample and mine was off just a bit. They then calibrated mine using calibration fluid and it matched spot on.

You really need to buy the calibration fluid ... it has a constant specific gravity of 1.0264 to calibrate your refractometer. It's only $8.00 a bottle.
I was still typing (I'm still a slow poke)and didn't see your post until I posted my response, you beat me to it good post.
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Old 09-29-2009, 08:17 PM   #9
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Here's a link to the calibration fluid were speaking of ...

Aquarium Testing Solution: American Marine Inc. 53.0 mS Calibration/Reference Fluid
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Old 09-29-2009, 09:21 PM   #10
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Yes, that is true, to be percise, you need the calibration fluid and to go further, be in a temp controlled room at the temp that the instruction say to be at. To add to this, pressure altitude (barometric pressure)will change the SG of liquids as well. All well within the margins we use in aquaria. A .001 +/- is close enough for most that the RO versus calibration fluid will generate.

Most meters are self temp correcting to temp but not to pressure altitude. Want to test it, watch the weather and as a storm approches use the calibration fluid and the once the storm is present, test again and it will be different. Probably more drastic that the differene between RO and calibration fluid.

In my feild, I us SG on a regular basis and have to adjust for temp and pressure.

But, I digress, if you want to do it totally right, use the calibration fluid, and you should test your refractometer rior to every use. It is probably best to use the fluid to make sure your meter doesn't go defunct.
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