Refractometer calibration

[bigbuckdown]

Ive been using distilled water for years and decided to try the calibration fluid now my question is can the calibration fluid be used on any type of refractometer or just the ones that say in the directions to use it. Mine said use distilled water and my tank calibrated with distilled water is 1.025 and with the calibration fluid its 1.021. should i stick with the distilled water because directions say to or go with the calibration fluid

 

[jimsplace]

Generaly the calibration fluid is correct because you are calibrating to a known value which is closer to what we keep our tanks at thus more accurate.

 

[DiscusHeckel]

Ive been using distilled water for years and decided to try the calibration fluid now my question is can the calibration fluid be used on any type of refractometer or just the ones that say in the directions to use it. Mine said use distilled water and my tank calibrated with distilled water is 1.025 and with the calibration fluid its 1.021. should i stick with the distilled water because directions say to or go with the calibration fluid

I always use distilled water with certified zero TDS. Equally important, I calibrate my refractometer after keeping it in a room temperature of 20C.

 

[swcc]

calibration fluid...generally refractometer that calibrate with zero tds RO/DI are required to do so being at an exact temperature for calibration and are often incorrect vs the solution which is a known salinity value... The salinity value also changes if the refractometer is a 'brine' or 'sea water' device.

 

[bigbuckdown]

So all known refracts that we use in our hobby can be calibrated with the solution. Well looks like i have to raise my salinity Anyone see a difference with SPS at a salinity of 1.021 and 1.025. is it that much of a difference in growth and color .004

 

[DiscusHeckel]

What is important is not the temperature of RO/DI, but the surface temperature of your refractometer. If you use salinity as opposed to gravity as the basis of your measurement, then the temperature of sample water should not matter.

Moreover, IMO, whether your device was calibrated with sea water or brine at factory is independent of how it should be calibrated by us.

I am sure I read one of RHF's articles in which he recommended RO/DI, but I may be wrong.

 

[disc1]

What is important is not the temperature of RO/DI, but the surface temperature of your refractometer. If you use salinity as opposed to gravity as the basis of your measurement, then the temperature of sample water should not matter.

Moreover, IMO, whether your device was calibrated with sea water or brine at factory is independent of how it should be calibrated by us.

I am sure I read one of RHF's articles in which he recommended RO/DI, but I may be wrong.

I'm positive that Randy never recommended using RODI to calibrate a refractometer.

You are absolutely correct that it is the temperature of the refractometer and not the water that is important. The small amount of water you put on there will very quickly come to match the temp of the crystal on the refrac. That's the reason the instructions usually say to wait a few seconds between putting the water on there and taking the measurement.

The reason the manufacturers say to do it with DI is because they don't know what you are going to measure, so that is the most sure point they can give you. But it is ALWAYS better to calibrate any instrument that only has a single calibration point as close to the actual measurement you intend.

It's about scaling. I've said this so many times it hurts. Many refractometers are scaled for saltwater and not seawater. Even ones that are sold as seawater refracs. Using a saltwater refrac that is calibrated at zero, a 35ppt seawater would measure 36.5ppt.

But if you calibrate with a 35ppt standard, then no matter what type of refrac you have, as long as it matches that standard you know you have 35ppt. That will always work out. Guaranteed.

Now, imagine the manufacturer said to calibrate to 35ppt, but you intend to use the refrac to measure a brackish tank at 1.010. Guess what, now the 35ppt calibration is as useless if not more useless than the RODI one.

If and ONLY if you check the refrac and it is true at two different values using the same calibration (say 35ppt AND zero) then you can assure yourself that the scale is right and you can calibrate it with anything you want.

 

[disc1]

If you use salinity as opposed to gravity as the basis of your measurement, then the temperature of sample water should not matter.
.

Not exactly. If you actually measured salinity then temp wouldn't matter. But there never has been and never will be a refractometer that measures either of those things.

A refractometer measures refractive index which is, incidentally, affected by temperature.

The salinity or specific gravity numbers you read on the scale are a conversion and they are based on some certain temperature. But at the same time, when we say keep the tank at 1.026 we mean at 20C. So if you measure the water at 18C and the refrac is ATC and says 1.026 then the water is right on. Because the refractive index has already been accounted for, and even though the specific gravity conversion is wrong, so was your target. If you were measuring at 18C you should have been targeting a lower value. But since you used a refrac and not a hydrometer, you don't have to worry because the conversion was assuming the right temp, even though that's not what you measured at.

Man that sounded confusing, but trust me the math holds out.

 

[disc1]

In addition to Randy saying it was bad to calibrate with RODI, he also gave a simple recipe to make your own calibrant.

3.65g of table salt (iodized is OK) + 96.35g of DI water makes a 36.5ppt saltwater solution. This solution will have the same refractive index as a 35ppt seawater solution and can be used to calibrate a refractometer to 35ppt.

 

[disc1]

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

Here's Randy's article BTW

 

[DiscusHeckel]

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

Here's Randy's article BTW

Thank you.

 

[bertoni]

Back to the first post... Which calibration solution is this?

 

[disc1]

Back to the first post... Which calibration solution is this?

You know, you bring up a good yet sorely overlooked point there.

 

[bigbuckdown]

standard seawater saline 35ppt

 

[klepto]

You know, you bring up a good yet sorely overlooked point there.

I couldn't agree more. It blows my mind how many hobbyists invest in new equipment/supplements/dosing pumps etc, and yet the effort and thought going into properly calibrating their refractometers is next to non-existent. :hmm2:

 

[bigbuckdown]

well thats why i figured its cheap enough to get a bottle and it will last for months. cost me 4 bucks for it. hell i spent 1500 on lights and a grand for flow whats 4 bucks LMAO

 

[bertoni]

If it's a seawater solution of some sort, it should be fine for calibrating the refractometer. We see reports of problematic calibration solutions from time to time, but that seems rare. I might get a second opinion, just out of caution. Randy's article will show you how to make one.

 

[kga943]

ok so i purchased some standard seawater saline 35ppt today and my refractometer was off so i set it to 35ppt and then checked my ro/di water and it was off so i adjusted it to zero then checked the 35ppt and seems to be pretty good at both readings so am i good to go now because my tanks do show higher then i thought

 

[Supra97]

ok so i purchased some standard seawater saline 35ppt today and my refractometer was off so i set it to 35ppt and then checked my ro/di water and it was off so i adjusted it to zero then checked the 35ppt and seems to be pretty good at both readings so am i good to go now because my tanks do show higher then i thought

I'm confused, you calibrated to 35, then calibrated to 0 with rodi, then with the calibration fluid again it read 35?

 

[kga943]

well when i first did the 35 i was pretty for off when i checked my tank so thats when i checked with ro/di so i adjusted again to 0 then checked the 35 and it was pretty good so i dont know if that is normal or if i just didnt get enough fluid on the first time ? but what i need to know is if i check at 35 with saline and 0 with ro/di i should be good to go ?