Refractometer calibration question

[Kairus]

Can I calibrate my refractometer using water from my LFS? They use NSW and confirmed with their refractometer that their water (at least what was filled in my bucket) is indeed 1.025.

[GHill762]

if you 100% knew for sure it was 1.025 then yeah you could.. but calibration fluid is like $2 and you know it's accurate.. I wouldn't bother with the lfs's water as a calibration fluid..

[sculptor]

I would not feel good about it. Plus you are supposed to calibrate to 35ppt anyway. I guess its better than no calibration at all.

[Kairus]

if you 100% knew for sure it was 1.025 then yeah you could.. but calibration fluid is like $2 and you know it's accurate.. I wouldn't bother with the lfs's water as a calibration fluid..

Good point, I just have to find some calibration fluid. None of my LFS sell any, they don't even sell refractometers, one of them tried to push me to get a hydrometer for $18.99 telling me they're accurate now because they have a 0 reading on them. I might have to make a trip to a further store.

[shifty51008]

http://www.bulkreefsupply.com/pinpoint-salinity-calibration-fluid.html

or if you have a good scale you can make your own
http://reefkeeping.com/issues/2004-06/rhf/index.htm

[thegrun]

I like this one better from BRS, it has a built in dropper that makes it easy to use, spill proof and you have almost no evaporation.
http://www.bulkreefsupply.com/catalog/product/view/id/861/

[icechimpee]

I like this one better from BRS, it has a built in dropper that makes it easy to use, spill proof and you have almost no evaporation.
http://www.bulkreefsupply.com/catalog/product/view/id/861/

+1 , this is what I've used in the past and it has worked out quite well.

[shifty51008]

I like this one better from BRS, it has a built in dropper that makes it easy to use, spill proof and you have almost no evaporation.
http://www.bulkreefsupply.com/catalog/product/view/id/861/

yes, that one also works great, it came with my new refractometer and is actually better to use because of the dropper, not that using the dropper from your refractometer is hard either :P

[cakemanPA]

I just mail ordered calibration fluid. It was a small price to pay for that peace of mind.

[Salty Dog24]

why not just use distilled water? Only $1 gallon!

[mitsu_matt]

If you use RO water it will be off. Not sure why but my RO water is much lower than the 35ppt in a bottle. 35ppt bottle and nothing else for the win.

[klwheat]

If you use RO water it will be off. Not sure why but my RO water is much lower than the 35ppt in a bottle. 35ppt bottle and nothing else for the win.

Hopefully your RO water is nearly 0ppt. Otherwise, you have a different problem.
Some refractometers actually say to calibrate with 0tds distiller water. Check the directions for yours.

[cakemanPA]

why not just use distilled water? Only $1 gallon!


RO is not an accurate way to calibrate

This is not a place to cut corners

[Patver258]

I use to calibrate with RO. After a thread like this one on an another forum, I went and bought some calibration fluid...

I was shocked by the difference, it was 1,028. All that time I thought i was at 1,025.

Patrick

[mattix]

My instructions say to use R.O. or distilled water. My R.O. is reading at 4 tds, working on getting it to 0. Why would I want to zero out my refractomerter at 35ppt?

[thegrun]

You don't zero it out at 35ppt, you align 35 to 35. A refractometer is no different than any other piece of lab equipmant, always calibrate as close to the anticipated result as possible.

[cakemanPA]

You don't zero it out at 35ppt, you align 35 to 35. A refractometer is no different than any other piece of lab equipmant, always calibrate as close to the anticipated result as possible.


This ^^^^^ +100

[reefer roman]

My refractometer directions say to use ro water or distilled also. Might have to try calibration solution to compare.

[disc1]

My refractometer directions say to use ro water or distilled also. Might have to try calibration solution to compare.

The reason the instructions say to use 0 is because the manufacturer doesn't know what you intend to use the refrac for. If you calibrate at 35ppt and then try to measure a hypo tank then you're going to be in just as bad shape.

Without knowing what you intend to measure, zeroing it is the best advise they can give.

But we DO KNOW what we want to measure. We want to see 35ppt seawater. So we can always beat that calibration by using a 35ppt standard.

This is an issue with any piece of equipment that only uses single point for calibration. You can't measure the slope of the response. So you aren't actually calibrating anything, you're just setting your scale so you know at least the one point is right.

Would you rather your refractometer have its maximum accuracy around 0 or 35ppt?

[GHill762]

yep, if you calibrate for 0ppt then it'll be accurate at 0ppt, but the farther you get away from 0ppt the less accurate it is.. it's seriously a couple bucks and will last you a long time..