What's the consensus on calibration fluid accuracy?

[NanoSteam]

Doing a search on R2R, I see the BRS calibration fluid being recommended over and over again but if you read the reviews on their website there are a lot of recent ones stating it's off by quite a margin.

I had a bottle of it come with my refractometer as a "kit". I did calibrate using it, had to make minor adjustment on the refractometer but how could I be sure it's actually accurate?
I was worried so I found the Fritz calibration fluid that had great reviews but no mention of accuracy this time. Using the Fritz fluid it says the BRS one is off by 5 PPT.

That's a large difference between calibration fluids. Which fluid should I believe? At this point I should just go back to a standard hydrometer that hasn't done me wrong in 15+ years. The uncertainty in my calibration is annoying me

 

[brmreefer]

Really hard to say as far as which one is more accurate. However, I would at least like to add that I use a calibration fluid (Advertised to be at 35 ppt = 1.026 SG) purchased from Amazon with no ill affects so far and I have been using it with no issues.

The part I really wanted to add to this reply is as follows:

• I check my refractometer against this fluid every 2 weeks, sometimes 3 weeks depending on how busy I get.
• When I check, I use a dedicated small pipette solely for the purpose of calibration checking to reduce any chances of cross contamination with any other liquids.
• I draw enough to do 3 or 4 calibration checks in one session.
• The first check I really ignore because I found that the first reading seems off a tiny bit.
• Then I take into account the next 2 or 3 readings as my more accurate readings.
• When performing the last reading, that is when I make any subtle adjustments and call it a day. Note: as long as there is really no significant differences with the 2 previous readings.

Temperature can be a factor too. I am pretty specific when testing as that is just personal preference. Maybe give it another go, but do several calibrations to see if the results are the same every time with one of the solutions, then do the same with the next one. Of course, that is if this method has not been already exercised. Best of luck and I'll be tagging along to see others chime in on their experiences with different calibration solutions.

 

[Ef4life]

im not going to say I’ve had issues with brs calibration solution but bottle to bottle (purchased and year or so apart) they were quite different.

I recently bought one of the tropic Marin hydrometers, no calibration needed. You just need to buy a graduated cylinder big enough to hold it.

My reef that was supposed to be 1.026 and I used brs calibration/refractometer - it measured 1.028 according to the new hydrometer. Even though it was high everything was perfectly happy and healthy and I slowly brought it down to 1.026.

 

[Reef - Tripp]

I use randy's recipe to calibrate and it's great, no more hesitation.

 

[Tman007]

Based on some recent surprises, I now trust Randy's recipe more than the store-bought calibration fluids...

I have two calibration fluids, from Brightwell and AquaticExperts, and they do not agree with each other, so I never knew which one to trust. Recently I got my first ICP-OES test results back from ATI, which indicated my refractometer reading was 5% high. Assuming that the ICP-OES results were accurate, I calibrated to that.

Based on this freshly-calibrated refractometer, here's how some other references compare, in order of accuracy:

1) Randy's recipe: within 1%
2) LFS#1* water (what they told me their water was at): within 1%
3) LFS#2* water (what they told me their water was at): within 1%
4) Hanna meter: refractometer reading 6% higher
5) AquaticExperts calibration fluid: refractometer reading 7% higher
6) Brightwell calibration fluid: refractometer reading 10% higher

(*both of my LFS are nationally known and R2R sponsors)

Bottom line: I'm no longer going to waste money on buying calibration fluids. If I don't have a recent ICP-OES test to calibrate to, I'll mix up a batch of Randy's recipe. Thanks @Randy Holmes-Farley !

 

[brmreefer]

Based on some recent surprises, I now trust Randy's recipe more than the store-bought calibration fluids...

I have two calibration fluids, from Brightwell and AquaticExperts, and they do not agree with each other, so I never knew which one to trust. Recently I got my first ICP-OES test results back from ATI, which indicated my refractometer reading was 5% high. Assuming that the ICP-OES results were accurate, I calibrated to that.

Based on this freshly-calibrated refractometer, here's how some other references compare, in order of accuracy:

1) Randy's recipe: within 1%
2) LFS#1* water (what they told me their water was at): within 1%
3) LFS#2* water (what they told me their water was at): within 1%
4) Hanna meter: refractometer reading 6% higher
5) AquaticExperts calibration fluid: refractometer reading 7% higher
6) Brightwell calibration fluid: refractometer reading 10% higher

(*both of my LFS are nationally known and R2R sponsors)

Bottom line: I'm no longer going to waste money on buying calibration fluids. If I don't have a recent ICP-OES test to calibrate to, I'll mix up a batch of Randy's recipe. Thanks @Randy Holmes-Farley !

Very nice! Thanks for sharing that. I'll be looking into Randy's recipe later on today as I am always looking for better or improved testing methods.

 

[piranhaman00]

To be accurate use a VeeGee and calibrate with RODI, calibration fluid is standard at 20C usually and refractometer ATC to 25C so you are off before you begin, only pure water is 0.000