How often do you calibrate your refractormeter??

[Myka]

I check mine about once a month. I check my clients' refractometers about once a month too. I find they all can use an adjustment by that time.

[mikellini]

I've read that light and temperature both have an effect on accuracy. For instance, if you're checking specific gravity on your water change mix in relation to your tank, you'll want to do it at the same temperature (unless you adjust for the difference) and definitely with the same light source.

It's probably more important to be accurate if you're running at 1.026, but if you run at 1.025 you have a bit more margin for error.

[Aquattro]

Originally Posted by mikellini

I've read that light and temperature both have an effect on accuracy.

I've tested the same water in kitchen under 100w lighting and against 800w of MH, same reading. And both my units are ATC, so temp shouldn't be a factor either.

[kamloops_reefer]

everytime - I have a vertex one and find that its a pretty touchy instrument. and can fluctuate +/- 0.03

[mikellini]

Originally Posted by Aquattro

I've tested the same water in kitchen under 100w lighting and against 800w of MH, same reading. And both my units are ATC, so temp shouldn't be a factor either.

From another forum (Randy Holmes-Farley, don't know if I can post the link):

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I was recently asked whether the light impacts the results one gets with a refractometer.

I'll give the rationale below, but it turns out it is CRITICAL that you use the same color light for calibration as for measurement. Don't move to a different room of your house where the lights may be different.

The reason for this is that the refractive index of water (fresh or salt) changes a lot with wavelength. The standard for all visible light refractive index measurements is supposed to be yellow (specifically, the yellow doublet sodium D line, with a wavelength of exactly 589 nanometers), but reefers rarely worry about such complexities.

The link below shows how much the refractive index of pure fresh water changes with wavelength (color):

Refractive index

specifically, here's a graph:



Look, for example, at the difference between deep blue (say, 480 nm) and orange (about 650 nm). Let's look at just the light blue line. That difference, from about 1.339 to 1.3325 is, remarkably, about the same as the difference between pure fresh water (RI = 1.33300) in yellow light and natural seawater (1.33940) in yellow light.

So the color effect on refractive index is as large as the entire difference between salt and fresh water.

However, we have a big saving feature at work. As long as you calibrate and measure in the same light (same color), the overall effect of the change in refractive index with light color largely cancels out between the calibration and the measurement, and you are able to sort out what portion of the effect comes from the added salts in the aquarium.

What you cannot do is calibrate under one type of light, and then measure tank water under a different set of lights (for example, in a room with fluorescents vs a room with incandescent lights or outside, or in a basement and then next to a tank with a lot of blue light.

Of course, rarely would someone have such extreme light differences as the deep blue vs orange mentioned above, but that is a 100% error in the salt concentration (ie., salinity might be really 1 ppt or sg = 1.001 when the refractometer says 35 ppt or sg = 1.026). I assume most reefers would like the salinity measurement to be far, far better than that, and so paying attention to the color of the light within the range aquarists might actually encounter is important.

So be sure and calibrate and measure in the same location if using a refractometer!

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And yes, theoretically if you have an ATC refractometer and it's working correctly, then you shouldn't have to worry about temperature. But if your refractometer is down in a cold basement, you might want to keep it upstairs just in case and bring it down to measure.

[mikellini]

Originally Posted by kamloops_reefer

everytime - I have a vertex one and find that its a pretty touchy instrument. and can fluctuate +/- 0.03

My vertex unit is touchy too. I calibrate with a 35ppt solution every time.

[Nicole.]

I never calibrated mine since the day I first got it which was prob a couple years ago...big mistake. Just recently had a buddy test my water and it was at 1.022 even though it would show as 1.025 on my refractometer. Who knows how long it's been at 1.022??! I've had a bunch of nice corals die and gave up on them because I couldn't figure out why at that time... Now I will calibrate mine after a couple uses. A bottle of proper calibration solution is only $5 so it's worth it.

[Slyguy00]

Originally Posted by mikellini

My vertex unit is touchy too. I calibrate with a 35ppt solution every time.

I'm with u guys. Pretty simple to keep calibrated so why not? The less fluctuation my tank sees the happier it will be as far as I'm concerned.

[jhj0112]

hmm maybe it's time for me to calibrate mine....

[SteveCGY]

Once every two years considering I use it once a month. And always leave it a point high so it compensates for evaporation and never let more than 4l absolute max evaporation. As soon as I can see water under my trim I add and add calcium to rodi water I ad