Calibrate with every use!

[treesprite]

This is a serious reminder of the importance of calibrating your refractometers frequently, because not doing it can crash your tanks.

 

When I had that high heat episode recently, I nearly panicked when I discovered also that my SG was way off. Then I remembered that temperature affects refractometer readings, so I re-calibrated, tested, and let out a huge sigh of relief. Now I calibrate every single time I use my refractometer.

 

Then this past weekend I got even more reason to take calibration seriously. I took my refractometer and calibration fluid to double check someone else's tank and refractometer, because she has had recent deaths while also her refractometer had not been calibrated in a long time. Her refractometer had been reading SG at around 1.024. I calibrated both refractometers then checked both tanks with both of them - the readings were between 1.035 and 1.040! I imagine that if we hadn't found the problem now, given how long the salinity may have been that high, that she'd have soon had total tank crashes.

 

Make calibration a part of your water testing routine, don't just take out the refractometer and assume that it will be on target today just because it was yesterday.

 

If you use hydrometers instead of refractometers, you can calibrate by comparing reading to a calibrated refractometer. Then check water that is at your target SG, and if the hydrometer "needle" is on a line with the wrong number, put the correct number there with a permanent marker. Do that as often as you can, but go get a refractometer as soon as you can - lots of them are inaccurate even when brand new, and the ones that are not will eventually get that way.

[Coral Hind]

That is a very good reminder! If anyone does still use a swing arm, it helps to soak it in vinegar every few months to clean it up so it gives more accurate readings.

[Happyfeet]

That is a very good reminder! If anyone does still use a swing arm, it helps to soak it in vinegar every few months to clean it up so it gives more accurate readings.

 

It also helps to throw it in the trash and buy a refractometer. Basically all my problems went away once I got a refractometer.

[Coral Hind]

That's a better option.

[Charlie]

I was trying to use a floating hydrometer. It worked great on set up, but as far as water changes and testing went, no so much. Having a refractometer made my life lots easier. HappyFeet's idea is right on the money, particularly when you consider how cheap refractometers are, eBay has them for around $30, or about the price of a weekend's worth of beer.

[Der ABT]

when calibrating your refractometer do you just use RO water and set it to 0? the calibration fluid i have makes no sense to as to what line it should be on.

when i use RO and set it to 0 it reads spot on with two other hydrometers (backups) and did it with a friends refractometer

 

I found mine on RC shipped for 15 bucks so it was hard to pass up.

[Coral Hind]

I just use RO/DI and set it zero.

 

Check out Randy's article.

http://reefkeeping.com/issues/2006-12/rhf/index.php#20

[Charlie]

when calibrating your refractometer do you just use RO water and set it to 0? the calibration fluid i have makes no sense to as to what line it should be on.

when i use RO and set it to 0 it reads spot on with two other hydrometers (backups) and did it with a friends refractometer

 

I found mine on RC shipped for 15 bucks so it was hard to pass up.

I just use the calibration fluid and turn the knob appropriately (I have to check the bottle, but I think that it's 1.030), then I rinse it with RO water.

[treesprite]

I have been using calibration fluid that says the reading should be at 35 ppm. Before I had that, I was using RO. Make sure it isn't an extreme temperature.

 

I would say put the old hydrometer in the tank junk closet as an emergency back up, because things do sometimes break at very bad times.

Edited May 28, 2010 by treesprite

[Origami]

It's best to use a calibration fluid rather than RO/DI to ensure accurate performance in the vicinity of your tank's salinity. This minimizes errors due to slope error (also called slope miscalibration in Randy's article linked above).

 

There are different calibration solutions available for different ways of measuring salinity. For example, there's a 53ms standard if you're measuring salinity using a conductivity measurement; there's a 35 ppt standard if you're measuring salinity using a refractometer (which measures refractive index); and there's a 1.0233 density standard if you're using a hydrometer (which measures density). The reason for the variety is that seldom, if ever, is calibration fluid made up of the complex balance of ions that make up "standard" sea water. Instead, it's often made up of a simple saline solution mixed to a specific concentration needed depending upon the calibration technique. Thus, the composition of each standard varies slightly depending upon what is being measured: conductivity, refractive index, or density.

 

You can see the effect of this in this RHF article: http://reefkeeping.com/issues/2004-06/rhf/index.php

 

In it, three recipes are given for DIY salinity calibration standards. (I've normalized the recipes below to illustrate the subtle difference in the standards used for different measurement devices.) Please note, a PSU stands for "practical salinity units." Our target is typically 35 PSU.

 

#1, 35 PSU refractive (refractometer) standard: 3.65 g table salt + 96.35 g water (yields 1.3394 refractive index)

#2, 35 PSU density (hydrometer) standard: 3.714 g table salt + 96.286 g water (yields 1.0264 density)

#3, 36 PSU conductivity standard: 3.29 g table salt + 96.71 g water (yields 53ms conductivity)