If YouUse a Refractometer You Should Read This

[bbyatv]

You should check your refractometer to see if it is a seawater or salt/brine version. As stated in the articles, most are salt/brine and will end up leaving the salinity in your tank low (around 33 ppt instead of 35 ppt).

 

Taken from these two RHF articles.

 

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

 

http://reefkeeping.com/issues/2004-06/rhf/index.php

 

Many refractometers are intended to measure sodium chloride solutions, not seawater. These are often called salt or brine refractometers. Despite the scale reading in ppt (

[BowieReefer84]

What refractometer are you now using?

[Origami]

Most of the refractometers used in this hobby are for brine. Thus, as Bruce notes, you need to be careful about what calibration solution that you use as 35 ppt NaCl brine does not have the same refractive index as 35 ppt artificial salt water. This is because of the different ions that make up ASW. The three most common ways that we "measure" salinity are:

 

Hydrometer

Refractometer

Conductivity meter

 

Each of these instruments measure something different about the physical characteristics of the fluid under test. In the case of the hydrometer, the characteristic is specific gravity (or density relative to water); in the second, it's the refractive index (how much it bends light); and, in the third case, it's electrical conductivity. Each of these is a different parameter and different calibration solutions, if not mixed to approximate the ionic composition of ASW, are needed to calibrate each of these devices. That's why Randy's article shows three different formulations of calibration fluid for these three devices.

 

The practical impact: Know what your calibration fluid is for. If it's a 52 ms calibration fluid (for salinity conductivity meters), it may not give you a true salinity reading in either a hydrometer or a refractometer. If it's formulated for a refractometer, it may not be useful to calibrate a hydrometer or a salinity conductivity meter. If, however, it's formulated with the proper ionic balance (meaning it's ASW), it should be applicable across all devices. Of course, the solution is more complicated to make and therefore more expensive.

[bbyatv]

Same one just calibrated for seawater using the calibration solution described in the article.

 

What refractometer are you now using?

[Origami]

I've toyed, at times, with the idea of bringing a big old jug to a meeting and mixing up some refractometer calibration fluid that people could take home. I'm sure that if we had a bunch of small bottles, we could do something like this pretty easily and cheaply. A lot of my lab equipment (including my scales) is still in boxes, though, from the move this summer.

[bbyatv]

This is a big discovery for me. I just mixed up some new Reef Crystals to 35 ppt with my newly calibrated refractometer and took parameter readings.

 

I got

35 for salinity - Refractometer

460 for calc - Salifert

1345 for Mg - Salifert

11.03 for Alk - Hanna

 

These almost match exactly what are listed on the Reef Crfystals box.

 

I used to have to add liquid calcium, baking soda and magnesium chloride to my new water parameters right at 35 ppt (prior to calibration for seawater).

 

Bruce

[Origami]

This is a big discovery for me. I just mixed up some new Reef Crystals to 35 ppt with my newly calibrated refractometer and took parameter readings.

 

I got

35 for salinity - Refractometer

460 for calc - Salifert

1345 for Mg - Salifert

11.03 for Alk - Hanna

 

These almost match exactly what are listed on the Reef Crfystals box.

 

I used to have to add liquid calcium, baking soda and magnesium chloride to my new water parameters right at 35 ppt (prior to calibration for seawater).

 

Bruce

 

That's great. It's good to know that they have their quality control on target. It also explains why the you were having to supplement in the past - you were mixing it too low, thinking you were at 35 ppt when, in fact, you were down closer to 33.

[RicSG]

 

Salinity Refractometer 0-28% Salt Water Aquarium ATC

http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=330415159106&ssPageName=ADME:L:OC:US:1123

 

Just bought this hope I am getting the correct product.

 

 

 

[Origami]

Salinity Refractometer 0-28% Salt Water Aquarium ATC

http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=330415159106&ssPageName=ADME:L:OC:US:1123

 

Just bought this hope I am getting the correct product.

I haven't a clue what %salinity means. Relative to what? 35 ppt salt water is 35 parts salt to 965 parts water, or 3.5%. I'm not sure how useful this particular refractometer is going to be. There are other, more appropriate, brine thermometers available.

 

It looks like it's a brix refractometer....

[bbyatv]

This is a brine refractometer (look toward the bottomof the listing). You will have to calibrate it like I did for seawater using RHF's calibration fluid for refractometers.

 

Bruce

 

 

Salinity Refractometer 0-28% Salt Water Aquarium ATC

http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=330415159106&ssPageName=ADME:L:OC:US:1123

 

Just bought this hope I am getting the correct product.

[Origami]

Here's an example of a brine thermometer that you would use in this hobby, if appropriately calibrated:

http://www.ebay.com/itm/RHS-10ATC-Salinity-Aquarium-Refractometer-Black-Rubber-/290585433068?pt=BI_Cellular_Optical_Television_Test_Equipment&hash=item43a83dd3ec

 

And here's one that's built specifically for seawater:

http://www.theaquariumsolution.com/seawater-refractometer