Calibrating a Refractometer with 53.0 ms fluid

[JohnS_323]

OK, so I picked up a bottle of calibration fluid. When I put it on my refractometer, I get about 1.028 for sg and 37 for whatever the reading on the right is (lol, never stopped to figure out what that means!). What should those be calibrated to with the solution?

TIA.

 

[sinkingbeach]

I was under the impression your suppose to calibrate with RO/DI ???

 

[Brian]

I was under the impression your suppose to calibrate with RO/DI ???

That's what the instructions say to do for my refractometer.

 

[sinkingbeach]

I was under the impression your suppose to calibrate with RO/DI ???

That's what the instructions say to do for my refractometer.

The Blue one from PA, right?

 

[AnDom1]

Hi John

Mine is an Auto Temperature Calibration model and I need to add drops os Distelled Water, wait 30 secs. then look into it for a reading of 1.00 on the left scale and/or 0 on the right scale. If above or below that level, I adjust by turning a setscrew
with the mini screwdriver provided. I suppose RO/DI water will also suffice.

Dom

PS What is 53.0ms fluid?

 

[JohnS_323]

We used the RO/DI method when we initally calibrated ours (which has always seemed accurate enough). Lately, though, there has been a good bit of commentary on here that says using RO/DI is fairly ineffective. I figured I'd a get a bottle of the 53.0 ms fluid and calibrate it "properly" to see if we get any significant variation in our results. I just need to know what the equivalent to 1.00/0 is using this fluid.

 

[AnDom1]

How about Distilled Water bought in the drug stoes?

 

[JohnS_323]

The reason I have heard not to use water (RO/DI or Distilled) is because with them, you are calibrating the refractometer at a range lower than the level where you will be seeing results for NSW. Since your tank water is going to be more in the 1.023-1.025 range, you'd want to calibrate it closer to that reading. Apparently, this 53ms solution is closer to the working range, so calibrating with it is *supposed* to make the refractometer more accurate. That's how I understand the case being made, anyway.

 

[JohnS_323]

OK, I got my answer. The numbers on the right are PSU or "Practical Salinity Units" (which have replaced parts per thousand). The PSU should be 35 with the calibration fluid. That is the same as 1.0264 sg. This is based on a temperature of 25*C.

Here is the link to the thread I got the info from in case you want to read more on the subject.

 

[billyr98]

boomer has always pushed, calibrating with that fluid, but i always did Ro/Di water..

 

[JohnS_323]

To be honest, both of our refractometers were off by so little using RO/DI that I can't imagine there being much of a difference either way. I'm not sure it's worth all of the hoopla. But the bottle was only $3 so it was worth doing the experiment, plus I have enough left to calibrate every refractometer in the club and then some.

 

[billyr98]

whats a little bit?

 

[JohnS_323]

The fluid is at 1.0264/35. Both of mine were calibrated with RO/DI quite a while ago and were at 1.027/36.

 

[roadking05]

Good info. Thanks

 

[billyr98]

cool thanks for doing the project for us, john!

 

[AnDom1]

Thanks John..Appears that the differences don't warrant concern (at least to me). I'll stick with distilled water as instructed by the mfr.

Besides going through that reference material gave me a headache :'( And all for a difference of 0.0006 :

But again thanks for investigating it for us.

Dom

 

[Carlo]

I always try and get people to calibrate with 53mS (35% salinity) solution because of this. RO/DI water just doesn't work well at all for most refractometers sold in the hobby. The difference of 35% and 37% is a HUGE amount. Think about it this way. For most Fiji/Tonga/Indo type corals you're 2%-4% over their normal average salinity. 37% is Red Sea range.

Now look at the advantage. $3 spent and you now have peace of mind and will save on salt from now on!

Carlo

 

[Phyl]

The fluid is at 1.0264/35. Both of mine were calibrated with RO/DI quite a while ago and were at 1.0271/36.

Carlo, I'm thinking you must have misread John's post. We're looking at a difference of .0007 (which ironically works out to be a .068% difference). Not enough, IMHO to even worry about. I'm sure my tank varies that much over the course of the day via evap! Turns out "calibrated" we'll actually be using more salt, not less. ::shrugs::

In any event we have the solution if anyone else wants to run through the motions.

 

[Carlo]

Unless I'm reading something totally different I thought John said he got a value of 37 % (right side of refracto dial) when he put the 53mS solution on it to test before calibrating it. If so that is 37 when it should have been 35 for a difference of 2% salinity.

Did I miss something?

I was thinking backward before however, you would be on the lower side of 35 now once calibrated, so now it costs you more for salt assuming you want it to be dead at 35. Lots of the low nutrient systems say 34 is best with 33-35 being the range. That also happens to match the Fiji area pretty well.

Carlo

 

[Phyl]

That one side can't possibly mean 36 percent (his initial post did say 37, but on further review the judges settled in at 36) or it wouldn't work out to a .068% difference between the two numbers. That number represents "Practical Salinity Units" which doesn't appear to be based in percentages. I'll have to go digging around and see what I can learn about the foundation of that PSU.