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02/15/2009, 11:19 AM
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#1 |
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Registered Member
Join Date: Jan 2009
Posts: 36
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Refractometer Question
I bought a fairly expensive refractometer to measure the salinity in my new tank and it measures 1.025 (even though I only put enough Instant Ocean salt in for 54 gallons and my tank is 65 gallons). My questions is can you just use these instruments out of the box like I did or do they have to be calibrated every time you use them. The instructions werent clear to me on this and I'm worried that maybe my reading is not true. Thanks.
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02/15/2009, 11:24 AM
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#2 |
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Registered Member
Join Date: Feb 2003
Location: South Jersey
Posts: 73
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what do you register with tap or r/o water?
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02/15/2009, 11:26 AM
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#3 |
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Registered Member
Join Date: Jan 2009
Posts: 36
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Zero
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02/15/2009, 11:28 AM
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#4 |
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Registered Member
 
Join Date: Feb 2006
Location: Palatine, IL
Posts: 2,652
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You should periodically calibrate them. I do mine every other month just to make sure. The solution cost very little.
 Here's an article on refractometers and includes a section on why you should use the solution instead of pure water to calibrate. I found that when using RO/DI to calibrate and then comparing to the solution I was off by .003 using the water. So I thought I was at 1.026 but was really at 1.023. Randy's article Last edited by drparker; 02/15/2009 at 12:07 PM. |
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02/15/2009, 11:30 AM
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#5 |
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Registered Member
Join Date: Jan 2009
Posts: 36
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Damn nothing is ever easy in this hobby is it? Thanks for the info!
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02/15/2009, 11:41 AM
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#6 |
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Registered Member
Join Date: Feb 2006
Location: Palatine, IL
Posts: 2,652
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It's simple really. The refractometer can have a slope error. Meaning the farther away from the calibration point your measuring the bigger the error can be. So if you calibrate to zero it will measure zero accurately but could be off when measuring 1.026. The solution allows you to calibrate to 1.026 and since that's where I want my mix I know it's accurate and don't care if it's off when measuring any other point on the scale.
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02/15/2009, 11:48 AM
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#7 |
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Registered Member
Join Date: Oct 2005
Location: 813
Posts: 2,827
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the link above takes me to a the pic posted, seems as though the copy of that carried over when drparker attempted to post the link. anyway, i believe this to be the link he intended to post:
http://reefkeeping.com/issues/2006-12/rhf/index.php at first i did not calibrate my refractometer, and when i did get the solution pictured above i found it was off by a lot, so it is very important to do this. the solution is cheap and the calibration is very easy so really there's no reason not to. 
__________________
order some golf shoes, otherwise we'll never get out of this place alive. what can i say? in dog beers, i have only had one. - dublo8 Current Tank Info: 40B aiptasia farm |
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02/15/2009, 11:56 AM
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#8 |
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Registered Member
Join Date: Oct 2002
Location: Punta Gorda, FL
Posts: 4,020
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I am tired of calibrating so I bought that glass hydrometer (with thermometer) for less than $4 at petco and use it to verify my reading on my refractometer. Many times, my refractometer is off. This alarms me to recalibrate. Sometimes I just prefer to use this inexpensive gadget. It is easier to use it when making fresh batch of saltwater. Trouble is, it is very fragile.
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The bitterness of poor quality lingers long after the sweetness of low price is forgotten. --------- No one is born with intellect and age guarantees wisdom to no one. Current Tank Info: 120G reef, 30G sump, 10G QT tank |
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02/15/2009, 12:11 PM
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#9 |
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Registered Member
Join Date: Feb 2006
Location: Palatine, IL
Posts: 2,652
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Yep, that's the one. Thanks for catching. fixed my link as well.
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