How often do you calibrate refractometer?

[Mightyfish]

Just wondering whether we need to calibrate refractometer on a regular basis or it is an one off calibration at the first time using it? If needs to calibrate regularly then what is the recommended period?

[CafeReef]

I test mine with RO every time before I test with SW, that way if I need to re-calibrate I know off the bat before adjusting my salinity. I have to tweek mine a .001-.002 every 3 weeks or so.

[fishgate]

Once in a blue moon. I checked about a week ago and it was still perfect after years. BRS cheap one.

[pdiehm]

I calibrate mine every time I use it. Just following the instructions on it.

[homer1475]

How is everyone calibrating? Using RO/DI or actual calibration fluid? If I use RO/DI I find that the calibration fluid is off by as much as .003. I stick with the fluid at a specific reading.

[Fish Keeper82]

I use some solution i bought from BRS it was less than 10 bucks and should last me very long time. It is calibration fluid set at 35ppt refractive index.

Its said to be better calibrated at a salinity close to what you are trying to measure as opposed to regular RO/ DI. Mine was calibrated before with ro di and when calibrated with the fluid i was off quite a bit it was like 1.023 with ro/di calibration and 1.020 after calibtating with the solution.
So basically i was .003 low for 7 years.
I will probably calibrate once every month or so. Bottle says every time your going to use but i think that's excessive.

[Fish Keeper82]

How is everyone calibrating? Using RO/DI or actual calibration fluid? If I use RO/DI I find that the calibration fluid is off by as much as .003. I stick with the fluid at a specific reading.


WOW i was writing my post any in that time you posted the same fluctuation.

[Marchillo]

Calibrating it takes less than a minute. I guess it depends on the quality of the refractometer. I got mine on the cheap and bought a bottle of the 35 ppt calibration fluid.

I don't have an ato yet so if I check it during the water mid week I may not calibrate it. But when making water I calibrate and match the tank water. It's usually not off by much at all if anything but it's not a bad idea to do often. So the short answer is once a week.

[Mark9]

How is everyone calibrating? Using RO/DI or actual calibration fluid? If I use RO/DI I find that the calibration fluid is off by as much as .003. I stick with the fluid at a specific reading.

Pinpoint calibration fluid from BRS, 8 bucks.
I calibrate maybe every 2 months.

[ReefsandGeeks]

Use the calibration fluid, not RODI. Hobbiest refractometers arn't 100% accurate across the whole scale, so you want to calibrate where you're going to measure. The more frequent you calibrate, the more accurate your results could be. Depends on the quality of your refractometer, and how well you handle it. If you're rough with measuring equipment it will not be as accurate. If you ever drop it, or hit it agenst something it wll need calibrated. Calibration is fast and cheap at home, I'd check weekly-monthly.

[coralsnaked]

Every time I use it and never w/ RO water always w/ calibration fluid. I wouldn't want to calibrate to zero w/ RO H2O as by the time the saturation has worked up to ~ 35ppm it is going to have a much larger % of error than if calibrated right at the point I want to use it at or near 35ppm. These meters have a fairly high static noise, I prefer to minimize it.

[amber3k]

I use calibration fluid and have only calibrated once in six months, that's when I first got it. I check it every so often but seems to hold pretty good.

[joshbrookkate]

I calibrate mine every time I use it. Just following the instructions on it.

Same here. With calibration fluid.

[ug.mac]

I also calibrate every time, for both optical and digital reflectometer.

[sleepydoc]

Here's (http://reefkeeping.com/issues/2006-12/rhf/index.php) a good article on refractometers & calibration.

In general, you should calibrate at or close to the point you're trying to measure, so using a calibration solution in most cases. If you're doing hypo salinity, RO/DI makes more sense.

I calibrate mine about twice a month - no real reason behind that interval, it just works for me.

[TangingOut]

For the people that say they calibrate every time, do you find it actually needs an adjustment?

Mine has held steady and for what it's worth, the temp in my house and tank remains pretty steady and I always jse the same light source.

[sleepydoc]

I haven't found a rhyme or reason as to when mine needs calibration. Sometimes it's spot on, sometimes it's off. It doesn't seem to be related to the time since the last calibration, though.

I have found that the light source makes a difference in how easy it is to read the refractometer but not the calibration.

[Mightyfish]

I used 35ppm solution to calibrate mine. Lets say if i want to use RO water to test my refractometer would it show 1 reading?

[peacetypes6]

bi-weekly

[kmbyrnes]

I check about once every 2 months. In 18 months I've only has to adjust 3 times.
My BRS refractometer has never been off by more than .002.

After a while you learn how much salt it takes make a batch in your mixing drum so you are rarely off by much in any case.

[jpa0741]

I used 35ppm solution to calibrate mine. Lets say if i want to use RO water to test my refractometer would it show 1 reading?

I believe it should read 0

[sellmecorals]

what is the average margin of error if uncalibrated?

[Fish Keeper82]

Uncalibrated???At minimum you should calibrate it with RO/DI and that in my experience was off .003 which is quite a bit.
if never calibrated there's no telling how far it could be off.

[tkeracer619]

Every time I use it.

[TangingOut]

Every time I use it.

It needs to be calibrated every time? Or do you just check it against calibration fluid every time? Big difference.

[Fish Keeper82]

Depends on meter and use .The solution says to calibrate every time but i check mine every month or so. I've only had to adjust it a few times and was not off by much.
some people say they have to adjust it more frequent.
if you're rough with it (drop it or so) it will need more frequent calibration

[sellmecorals]

People are saying to calibrate with liquid at a similar salinity, but RODI is 0.0000 salinity?

[TangingOut]

People are saying to calibrate with liquid at a similar salinity, but RODI is 0.0000 salinity?

Calibration fluid is 35pt which is 1.026 sg and that's why it's preferred over RODI.

[m0nkie]

I've been getting lazy.. I calibrate with calibration fluid. Probably haven't done so in 2-3 months. I recalibrated it again yesterday and it was off by 0.001 - 0.002.. not too bad

but I'm very careful with handling the equipment. If i drop it or something, I would recalibrate it again

[sellmecorals]

Would my tank water, which I'm trying to test, be a better calibrator than Rodi Water because it's the ballpark salinity?

[ca1ore]

I only calibrate mine when I'm looking to get an absolute reading. Most of the time I'm comparing two samples, thus making a relative comparison, so I don't bother.

[JoeDaReefer]

I got mine used ($13) from a local two years ago, and just recently calibrated it after learning that it can get off over time.

It read 1.0245 instead of 1.026, so no issue there. To anyone curious, it is the Red

[sleepydoc]

You cannot use the tank water to calibrate because you don't know what the specific gravity is. If you did you wouldn't need to test it.

How often you need to calibrate depends on the refractometer and other factors. I have found no consistent pattern to how fast or how far mine drifts out of calibration. Since you need to check calibration periodically regardless, you should have calibration solution on hand. It takes less than a minute to check, so there's not much reason not to.

You should calibrate with a solution close to that you're trying to measure. For most applications, the standard 35ppm/1.026 solution is the most appropriate. If you are running hypo salinity, RO/DI (0 PPM/1.000) would be better.

In a pinch you *can* use RO/DI if you don't have calibration solution, but the farther away you get from the calibration point, the farther off you are likely to be, so spending a couple bucks on a bottle of calibration solution is a good investment.

[tkeracer619]

Just check it. It stays pretty true but needs adjusting maybe twice a year. Mine gets a lot of use and gets tossed around quite a bit.

[sellmecorals]

Doc, I get the need to check the level to know the level, but I'm sure my tank water is closer to my desired ppm than Rodi water. Yet Rodi is a better calibrator?

[tkeracer619]

Of course, you can't calibrate a refractometer with the water you are trying to test. That would be like taring a scale with what you are weighing already on it. If you wanted all of your tanks to match one tank then sure, cal it to that tank but you still don't know what that tank actually is.

The purpose of calibrating is to reference a known point. RODI is known it's just not close to the 35ppt you are looking for. Though, that probably doesn't even matter much because it will likely get you into the safe range and as long as the tank is in a safe range you are fine.

[firstlight10]

I try to do it every 30 days or so, that's an easy interval to remember.

[sleepydoc]

Doc, I get the need to check the level to know the level, but I'm sure my tank water is closer to my desired ppm than Rodi water. Yet Rodi is a better calibrator?

the whole point of a calibration solution is that it is known (and consistent.) Not only is your tank salinity not known, it potentially varies over time.

Even if you use RO/DI, the error when reading at 1.026 (or whatever your tank is) will usually be small enough to be tolerable, and more importantly it will stay the same.