Refractometer Calibration

[Spartanwarrior]

Hey All,

I profess to be no expert on Chemistry. I like to think I have a rudimentary knowledge so I pose this question.

I've been researching the correct way to calibrate a refractometer. By all expert opinions I find, the majority says spend the $10 on calibration solution, or make your own with table salt and RO mixture. Fine.

I did and have been for years using a calibration solution for 35ppt. However, I'm having an issue with a new salt (aquaforest) giving my ultra low alkalinity readings (sub 6.5dKH). I posed the issue with Aquaforest and their expert has told me my measuring must be off, blah blah...that is neither here nor there.

It got me to thinking, what if my calibration solution is off? What if evaporation has begun to affect the solutions salinity?

So my question is this, can I confirm my calibration results by using RO water and getting exactly 0ppt? The reason I ask is, I tried that and I got a reading below 0 ppt so that I had to adjust the setting on the refractometer back up to zero. However, when I checked the calibration solution again, it measured about 1.029 or close to 40 ppt. If I'm way off, poke fun at me, but it seemed like a reasonable assumption to me.

Thanks all.

 

[edd]

my sybon came with ultra pure water to calibrate to 0.
i read that you can use rodi. they also sell sea water cal fluid that you adjust to 35

 

[Spartanwarrior]

not quite the answer to my question, but thanks for the input. I'm wondering if I calibrate with Calibration fluid and RO water, should I get 0 with the RO and 35ppt with the solution when used back-to-back? B/c I don't. Wondering if something is off or is my chemistry off.

 

[marrone]

If you use RO/DI water you should get 0, with the calibration fluid you should get either 34 or 35ppt, don't remember which as I need to look at the bottle that I have home to be sure. It's possible that the calibration fluid is old or you have some evaporation which would make the reading come up higher than what it's suppose to be.

 

[Spartanwarrior]

thank you Marrone. Exactly the answer I was looking for. I figured the logic was sound, but I was off almost 4 ppt so thought the math might not equal up. I'll use some NutraSeawater to test as I wait for the new calibration fluid.

 

[edd]

their is also calibration fluid that reads 0, like i mentioned that came with my sybon.
you need to know witch one you have.

 

[Spartanwarrior]

Its 35ppt

 

[reefiness]

sounds like bad calibration fluid. Best bet IMO is get a fresh bottle of calibration fluid and calibrate to that.

 

[seldin]

Buying calibration fluid is not necessary, just get rodi water and set refractometer to 0. As a test, I tested with calibration solution and rodi water and got the same result.