Salinity question.

[aquamann183]

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Refractometer is ATC brand.

Which do I trust? Two completely different numbers.

Thanks!

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[CindyK]

I've never used a hydrometer but when did you last calibrate the refractometer?

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[aquamann183]

I've never used a hydrometer but when did you last calibrate the refractometer?

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I never have, just tried using it today. How do I calibrate? I thought it was supposed to come with a solution or something.

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[ALLIDOISREEF]

I would trust the refractometer over a hydrometer. As long as its been calibrated.

[aquamann183]

I would trust the refractometer over a hydrometer. As long as its been calibrated.
Has not been calibrated. I will have to look into how I go about doing that.

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[minus9]

Buy some calibration fluid (35ppt) and calibrate the refractometer. Hydrometers can never be trusted.

[toddarcham]

You can just use distilled water on some refractometers and set to 0 by turning the little screw on top.

[aquamann183]

You can just use distilled water on some refractometers and set to 0 by turning the little screw on top.
Can I use my rodi water?

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[toddarcham]

Can I use my rodi water?

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Pretty sure you can. The DI makes it pretty pure.

[CarrieB]

You can use RO DI water, but the calibration won't be as accurate as using the calibration fluid.


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[RogueGrown]

I've wondered this as well. Yes distilled will calibrate to 0, is this true for DI water as well?

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[Finland]

I would recommend buying some 35ppt calibration fluid and not using ro water. RO water is not a reliable way to calibrate a refractometer. Calibration fluid is cheap in relation to the rest of this hobby, so why risk it?

[slief]

The Hydrometer is likely not accurate. They never are. Calibrating a refractometer with distilled water for our SG target levels isn't ideal and won't be very accurate. RODI will be less accurate. You should really use 35ppt refractometer calibration solution.

If you really want an accurate measurement with your refractometer, get yourself a bottle of this and keep it at room temperature.
http://www.marinedepot.com/Two_Little_Fishies_AccuraSea_Seawater_Reference_and_Calibration_Solution_Calibration_Fluid_Reagent-Two_Little_Fishies-TL50700-FITECL-vi.html

[Ou8me2]

Yeah, you need salinity calibration fluid. However, I buy mine at BRS it's a lot cheaper. Once you get it calibrated with the solution you should be able to not worry but I do check once a month to make sure it's still on target where I want it to be salinity wise. You only need a couple drops and that small bottle will last a long time. If you buy the refractometer at BRS they include the calibration fluid which would be silly if you didn't actually need the calibration fluid. :D

http://www.bulkreefsupply.com/aqua-craft-refractometer-calibration-fluid.html

[aquamann183]

Okay, thank you all! Buying some fluid now!

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[slief]

Yeah, you need salinity calibration fluid. However, I buy mine at BRS it's a lot cheaper. Once you get it calibrated with the solution you should be able to not worry but I do check once a month to make sure it's still on target where I want it to be salinity wise. You only need a couple drops and that small bottle will last a long time. If you buy the refractometer at BRS they include the calibration fluid which would be silly if you didn't actually need the calibration fluid. :D

http://www.bulkreefsupply.com/aqua-craft-refractometer-calibration-fluid.html

That is cheaper but it's also about 1/4 the volume (60ml) for about half the price. You get 4x as much (250ml) for about double the cost with the TLF stuff. Granted BRS does have free shipping even on smaller orders. I think I'd trust the TLF stuff to be a bit more accurate/consisnt simply becaue I trust Julian Sprung. I've had inconsistent results with some other calibrations solutions where 2 different bottles were different salinites despite both being 53ms. Those were PinPoint if I am not mistaken though.

Okay, thank you all! Buying some fluid now!

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Good choice! You won't have to question your results anymore. :beer:

[taricha]

Or...
1. Mix up your reference solution with table salt
" a solution of 3.714 weight percent sodium chloride has the same specific gravity (and density) as S=35 seawater, and can be used as an appropriate specific gravity standard "
To do this, 37.14g of salt into 962.86g of distilled water (total mass - 1000.0g)
From RHF (http://reefkeeping.com/issues/2004-06/rhf/index.php)
2. Mark the line where that salinity = 35 solution registers on your swing arm. (On my swing arm it's right below "32 ppt")
3. That line is your new target line.

Swing-arms aren't accurate, but they are pretty dang consistent, if you avoid bubbles.

[Twoface14]

You also need to fill the hydrometer up to the fill line to get a more accurate reading. In your picture it is well below

[aquamann183]

You also need to fill the hydrometer up to the fill line to get a more accurate reading. In your picture it is well below
You're right, I just did it quickly because I checked it earlier before that and already knew it was off before adding water to the hydrometer when I checked it.

What about the little things that you put in the water that floats at the certain specific gravity. Besides the fact that they're not the easiest to read, how accurate are those?

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[jason2459]

Or make your own calibration fluid which can be more reliable then a store bought calibration fluid.

Does your calibration solution need calibrated?
http://www.reefcentral.com/forums/showthread.php?t=2583418


Using RO/DI or distilled water for many of the refractometers sold in this hobby will not work as many are not true seawater refractometers and will be off near the point we want to measure (~35ppt). Even with a true seawater refractometer like the veegee/vital sine or the milwakee digital that can be calibrated at 0 it's a good idea to use a 35ppt calibration fluid to double check accuracy near the point we want to measure.

Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/

[ktownhero]

I wouldn't trust the hydrometer even if the refractometer is uncalibrated. Get that thing calibrated and toss the hydrometer. Seriously, toss it... :)

[jason2459]

I wouldn't trust the hydrometer even if the refractometer is uncalibrated. Get that thing calibrated and toss the hydrometer. Seriously, toss it... :)

A swing arm hydrometer if matched and marked against a known point of reference at the right temp can be used just fine. In the end our corals can adapt to a wide range of salinity. Keeping salinity at a certain point near 35ppt is the best thing we can do but even if you think you're at 35ppt and you're say 34ppt or 36ppt you'll be just fine keeping it there.

Pick a method to test for salinity, pick a method to calibrate for near the point you want to keep, and pick a method to keep it there. Then keep that consistent.

and personally, I'm not a fan of swing arm hydrometers myself.