I keep learning thanks Jagermeister

This is a great thread. Of course, none of us have certified instruments for measurement of the calibration solution, so we all probably have some amount of error. I have a kitchen scale that measures in grams, and who knows how much error it has. Here's how analytical I got with the scale to check it - I took a stick of unopened butter in it's wrapper that is supposed to be 113 grams and my scale said it was 114 grams. Woo-hoo, it must be accurate!

I think Roadracn has the best idea - go out and buy a calibration solution. R - have you found a place locally to buy some or did you order thru the mail? I would take you up on your offer but I live up in Thornton.
 
I work in Commerce City, so I'm there every day. At least that is closer than Thornton. Maybe I could meet you somewhere. I am also in on the invert order that Chris (Katyttt) handled, so will be driving to his place Thursday to pick up the new inhabitants. Were you part of that order too?
 
I want to say thanks also. When I bought my refractometer I calibrated it according to the instructions thinking that the manufacturer would know best. However, I made the calibration solution (the one in Randy's article using 2-liter bottle) using RO water of the same temperature as my tank. My refractometer was apparently reading 5 ppt too low! The salinity in my tank was roughly 1.021. I did the math - to bring my tank up to 1.026 I need to add roughly 8 cups of salt.

BTW - a comparison my salinity checkers....my hydrometer was reading 1.025, my floating salinity monitor read 1.020 (which I have always disregarded as a POS), and my refractometer had been reading 1.026.

I have about 2 liters of extra solution - I kept a small bottle for myself to be used in the future. If anyone wants to take some DIY calibration solution and lives near Highlands Ranch, shoot me a PM. You are welcome to fill a bottle.

Thanks again! I hadn't ever read any of the calibration articles because I had assumed I was doing it right.
 
I got th pinpoint stuff yesterday. It doesn't match the DIY but I am going to make a new batch and be supre careful, unless miwoodar wants to come over and we can check it with mine?

Curt
 
Well, u know what they say, when all else fails read instructions. My refractometer came with a very detailed operation manual. It is an ATC (auto temp calibrating) salinity refractometer designed for testing the "concentration of saltwater and brine in the marine industry". Step one in the manual says calibrate to null with RO water. So per the instructions I put 2 drops on the glass face, waited 30 seconds to temp cal, and then adjusted it to zero. I then took my 2L calibration solution I had made up and put 2 drops on the glass face and waited 30 seconds - voila it read 1.026. When I checked my aquarium it read 1.029! Much too high. I also purchased some American Marine Pinpoint Salinity calibration solution, so I'll see how that compares when it gets here.

I also talked to Animal Attractions yesterday and they had asked several of their suppliers about calibrating refractometers. They all said calibrate with RO water. So maybe it depends on your particular refractometer and whether it is designed for testing salt water. I know the manufacturer of mine makes them for the battery acid industry, fruit juice industry, sugar industry, clinical labs and others.
 
like i said r.o. will work at 60 degrees(the refractometer not the water... four drops of water changes temp quick) but the higher the temp the lower the specific gravity. the link i posted should have explained that. at room temp the specific gravity drops to .998. if you are calibrating with r.o. at 80 degrees then you would probably have a .005 average of being wrong on the low side.
 
as long as the Frac is room temp, and the calibration solution is the correct temp, the calibration should be accurate.
 
so i went over and checked out my hydrometers at roadracn's place tonight. against his finely and accurately calibrated refractometer. they were both within .001 of the refractometer. ive been using these for two years and have never done anything but rinsed them before and after use. i think i like my $20 invested... now time to up my salinity a little as it sits at 1.022:)
 
I was following this thread and found it to be very interesting. I went ahead and made the homemade calibration solution and tested it out. It showed my salinty to be a little lower than I had originally thought, which could explain a few things that have been occuring in the tank. I do plan on checking it against a friends refac before I go adjusting things too much.
My question is, is that with the refrac calibrated using the 1.026 solution, should it also read 0 when testing it with RO? Mine is way below the 0 line when calibrated to 1.026.

Janice
 
Theoretically, it should read 1.000 (35 ppt). What I have recently learned (thanks again to this thread) is that hobby grade refractometers will often read low against RO/DI water if they have been calibrated against a higher concentration. They will be most accurate at concentrations closest to the one they were calibrated for.
 
It should read 1.000 with plain tap water, unless you are using well water!

Interesting thread.... remember that you can use any liquid to calibrate with, as long as you know the SG of the test liquid within a certain degree of accuracy. A simple saline solution from the pharmacy works (isotonic is OK too). Hmm... I'm going to have to break out my old CRC Handbook.... I knew there was a reason that I kept that! :)

I would agree that when calibrating for lab conditions that using a calibration fluid close to the value you expect to be testing would most likely yield more accurate results.

I'll play around a bit with mine using known solutions and see what I come up with. I'd like to hear more results from other folks.

-Rob
 
FYI...

I picked up some of the Pinpoint 53µS calibration solution. I check my DIY calibration solution against Pinpoint's solution. I was off by .001 (1.025 DIY - 1.026 Pinpoint). Not bad.
 
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