Refractometer Question

[babarney]

I recently aquired a used refractometer and was wondering how you clean it. I am assuming that in order to keep the readings as accurate as possible the salt water needs to be cleaned from the lense but I don't want to do anything to damage the device. Could I just rinse it off with RO water and dry it with a paper towel, or should I let it air dry? Thanks!

[spieg]

Yep, RO water and a clean cloth would be fine. Mine came with a cleaning wipe kind of like what comes with sunglasses. Even so, I more often than not just use a clean towel or a paper towel to wipe it off.

[Pufferpunk]

Be sure it's calibrated with RO calibration solution or it's worthless.

[DustinB]

I just dip one end of a paper towel in RO water and softly wipe the lens and around the lens. The with the dry end lightly go from one side of the lens to the other a couple times until it's dry. Paper towels can scratch if you rub too hard or if you allow the saltwater to dry. Just do it lightly and do it immediately after testing. Be sure to clean the cover plate too.

[DustinB]

How is it worthless without the solution? I use RODI water to calibrate mine.

[Pufferpunk]

It'll be close with that, but not exact: http://reefkeeping.com/issues/2006-12/rhf/index.php

[mr.maroonsalty]

If you want precisely 1.0264 ro won't get you there because water itself has a different refractive index than synthetic salt water; I think its fine if all you're after is consistency, as reefs are found at many different salinity. I use calibration solution, as it doesn't cost much.

[DustinB]

If I am reading 1.026 right now, how far could it be off? I guess I might try to grab some solution.

[Pufferpunk]

Depends on what you're keeping in your tank. Some corals are more demanding of exact parameters than others.

[babarney]

The guy I bought it from calibrated it to 0 with RO water right before I got it. I am basically looking to keep the water at 1.025. Will this method keep the water close enough or should I buy calibration fluid?

[DevilBoy]

i would not use ro water to calibrate with. yea it might read 0 . your best bet is to buy calibration solution. they sell it as 53.0 mS solution, and calibrate refractometer at 35ppt with this solution.

[mr.maroonsalty]

I'll say consistency is more important than the 1.026 average.

[spieg]

After calibrating with calibration solution, RO water reads quite a bit less than 0PPT on my refractometer. I wouldnt trust RO as a calibration. That said, ive heard of plenty of calibration solutions having bad batches and being off as well, but id rather take my chances with that than trust RO getting me close enough.

[Njkidd23]

The soulution is only like 8$ and will last years might as well spend it

[Pufferpunk]

You'll be the most popular guy in your reef club, if you offer to calibrate everyone's refractometer!

[drew1]

Distilled water works fine for calibrating to 0

[Pufferpunk]

Did you read that Reefkeeping link?

[drew1]

Yep. Its simple science - light refracts differently at different densities. If you test at more than one known point on a scale you'll get better accuracy - usually well within the margin of error. Like the link says: 1. First calibrate the refractometer in pure freshwater. 2. The second step in calibration .... testing it in a solution matching the refractive index of 35 ppt seawater.
One point will be fine (distilled water), two points will be better.

[spieg]

Originally Posted by drew1

Yep. Its simple science - light refracts differently at different densities. If you test at more than one known point on a scale you'll get better accuracy - usually well within the margin of error. Like the link says: 1. First calibrate the refractometer in pure freshwater. 2. The second step in calibration .... testing it in a solution matching the refractive index of 35 ppt seawater.
One point will be fine (distilled water), two points will be better.

I could be wrong, but I think that when the author mentioned more than one calibration solutions, pure water was not being considered as a calibration solution. I know that when I calibrated mine using RO water, and then tested its accuracy using a 35ppt calibration solution, it was off. Maybe my calibration solution is bad (I bought it a month ago), but I dont trust RO to calibrate my refractometer.

[Pufferpunk]

Heck, it's your tank, do as you wish.

[drew1]

The two steps that I listed are directly from the link, at the bottom of the link:

Tips on Calibrating a Refractometer

--------------------------------------------------------------------------------

Despite the fact that many refractometers sold to aquarists recommend calibration in pure water, such a calibration alone will not ensure accuracy for the reasons described above. So my recommendation for calibration is as follows:
1. First calibrate the refractometer in pure freshwater.
2. The second step in calibration .... testing it in a solution matching the refractive index of 35 ppt seawater.

You don't need to make this more complicated than necessary.

[spieg]

Im not trying to complicate things or arguing with you, im more curious than anything. I found it odd that when I first calibrated with RO and then checked my calibration fluid it read higher than 35ppt. So I ended up just recalibrating with the calibration fluid and calling it good. Now, if I test RO, it reads under 0. Hopefully my tank isnt really at 40ppt or anything!

[drew1]

I'm with you. I hope your salinity is good. Really this is just physics. Refractometers use light rays to measure the density of water. Hydrometers use the density of the water to float a piece of plastic of a calibrated weight. The fact that this binds up ocasionally or breaks off is the flaw with the hydrometers. I usually use a hydrometer for a sanity check. If you question the result of your refractometer you might want to check your results with other sources (friends, LFS, etc) or get a hydrometer.

[hillscp]

I think the section in the article titled

"Imperfect Refractometer Calibration: Slope Miscalibration"

Covers the problem. I recently got the BRS refractometer that came with the calibration fluid. The instructions provided by the manufacturer said to calibrate with distilled water but BRS put a sticker on the box that said not to calibrate to zero and use the standard. The instrument came calibrated to zero. The calibration fluid read 1.039. I calibrated to the fluid after reading the article and now ro/di reads below 1.000.

The problem is that those cheap refractometers have a slope error but it doesn't matter if you calibrate with a standard that is the same as your sg goal.

[Pufferpunk]

Originally Posted by spieg

Im not trying to complicate things or arguing with you, im more curious than anything. I found it odd that when I first calibrated with RO and then checked my calibration fluid it read higher than 35ppt. So I ended up just recalibrating with the calibration fluid and calling it good. Now, if I test RO, it reads under 0. Hopefully my tank isnt really at 40ppt or anything!

That's not at all how it works!