Homemade vs. "store bought" Calibration Standards

vames · 11/06/2009, 11:28 AM

I recently bought a refractometer, and used the method described here:

Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.htm

to make a homemade calibration standard in a 2-liter soda bottle and used it to calibrate my refractometer. Before I did this, there was a pretty large discrepancy between my swing arm hydro, glass float hydro and the new refractometer (both hydros were about the same, refract was about 0.02 higher). When I used the standard, it also read higher than expected, which was good in my mind since that agreed with the discrepancy. Now all 3 read very closely, which I like. However (and boy, that's alot of background for the upcoming question....sorry), I'm wondering if anyone has ever tested the homemade calibration standard vs. a store-bought standard. I'm pretty satisfied with the homemade, but in the back of my mind, I'm wondering....

Anyone?

Evil Nemo · 11/06/2009, 11:43 AM

I've found the accuracey the same in both formulas. Never had a hydrometer for salinity. IMHO they are only good for checking 1966 Dodge truck batteries.

old salty · 11/06/2009, 11:57 AM

In my previous job, I had access to some seriously accurate scales and measuring equipment. I made a few standards, and also purchased standards from several companies such as Pinpoint and Aquacraft. They are all pretty darned close to each other and the animals in my tank don't seem to mind a small shift in salinity.

If you and I purchase the same salt and the same test kits, but we calibrate our refractometers with different solutions, the end test results may demonstrate the disparity. Again, I don't think the difference is really enough to affect the animals, but you may have a small issue with obtaining repeatable results if you change calibration solutions prior to each test.

Raggamuffin · 11/06/2009, 01:09 PM

I just used dasani to calibrate, ended up being 0.001 off close enough for me

Zero'd out with the dasani, tested tank water which 3 of my friends all got 1.025 and came up with 1.026 adjusted and ta da all good.

Randy Holmes-Farley · 11/06/2009, 02:33 PM

If you have a good scale and volume measuring devices, your DIY standard will be as good as any you can buy.

If you are using coke bottles, the standard will be potentially less accurate, but suitable for ruling out gross errors.

FWIW, you can buy (or borrow) the Pinpoint 53 mS/cm standard, and compare the DIY to it. Maybe get a slightly revised value for the DIY, if necessary, and then you can use that DIY in all sorts of ways, like passing it around to around to anyone that wants it, scaling up to larger devices, etc.

Randy Holmes-Farley · 11/06/2009, 02:36 PM

I'm wondering if anyone has ever tested the homemade calibration standard vs. a store-bought standard.

When I designed the standard, it was developed using exact values from the scientific literature. It does not depend on a store bought standard (and they were not available to hobbyists at the time anyway), but folks who have compared them find them the same (when made to the weight based recipe).

vames · 11/06/2009, 02:50 PM

Quote:

Originally Posted by Randy Holmes-Farley

I'm wondering if anyone has ever tested the homemade calibration standard vs. a store-bought standard.

When I designed the standard, it was developed using exact values from the scientific literature. It does not depend on a store bought standard (and they were not available to hobbyists at the time anyway), but folks who have compared them find them the same (when made to the weight based recipe).

That's good info Randy, thanks. I did not, however, use a weight-based recipe (I have a home scale, perhaps I'll try it), but I used the 1/4cup + 1tsp. of salt dissolved in 2liters of water (I actually measured out 4x500mL from a pyrex cooking measuring device rather than trusting the 2L bottle to be 2 liters.) Anyway, I'm comfortable that it's good enough to keep fish alive, but wondering how well it might compare to a store-bought standard.

I'll probably do as suggested and borrow a drop from a fellow local reefer who owns a PinPoint or other brand standard. Thanks!

Randy Holmes-Farley · 11/06/2009, 03:03 PM

That sounds good.

Let us know how it compares for you.

11/06/2009, 11:28 AM	#1
vames Registered Member Join Date: Aug 2009 Location: NW Indiana Posts: 75	Homemade vs. "store bought" Calibration Standards I recently bought a refractometer, and used the method described here: Reef Aquarium Salinity: Homemade Calibration Standards http://reefkeeping.com/issues/2004-06/rhf/index.htm to make a homemade calibration standard in a 2-liter soda bottle and used it to calibrate my refractometer. Before I did this, there was a pretty large discrepancy between my swing arm hydro, glass float hydro and the new refractometer (both hydros were about the same, refract was about 0.02 higher). When I used the standard, it also read higher than expected, which was good in my mind since that agreed with the discrepancy. Now all 3 read very closely, which I like. However (and boy, that's alot of background for the upcoming question....sorry), I'm wondering if anyone has ever tested the homemade calibration standard vs. a store-bought standard. I'm pretty satisfied with the homemade, but in the back of my mind, I'm wondering.... Anyone?

11/06/2009, 11:57 AM	#3
old salty Genius Join Date: Jun 2005 Location: The Island of Misfit Toys Posts: 3,131	In my previous job, I had access to some seriously accurate scales and measuring equipment. I made a few standards, and also purchased standards from several companies such as Pinpoint and Aquacraft. They are all pretty darned close to each other and the animals in my tank don't seem to mind a small shift in salinity. If you and I purchase the same salt and the same test kits, but we calibrate our refractometers with different solutions, the end test results may demonstrate the disparity. Again, I don't think the difference is really enough to affect the animals, but you may have a small issue with obtaining repeatable results if you change calibration solutions prior to each test. __________________ "The man who reads nothing at all is better educated than the man who reads nothing but newspapers." Thomas Jefferson Current Tank Info: Out of the marine aquarium hobby

11/06/2009, 02:33 PM	#5
Randy Holmes-Farley Reef Chemist Join Date: Apr 2001 Location: Arlington, Massachusetts Posts: 86,233	If you have a good scale and volume measuring devices, your DIY standard will be as good as any you can buy. If you are using coke bottles, the standard will be potentially less accurate, but suitable for ruling out gross errors. FWIW, you can buy (or borrow) the Pinpoint 53 mS/cm standard, and compare the DIY to it. Maybe get a slightly revised value for the DIY, if necessary, and then you can use that DIY in all sorts of ways, like passing it around to around to anyone that wants it, scaling up to larger devices, etc. __________________ Randy Holmes-Farley Current Tank Info: 120 mixed reef

11/06/2009, 02:36 PM	#6
Randy Holmes-Farley Reef Chemist Join Date: Apr 2001 Location: Arlington, Massachusetts Posts: 86,233	I'm wondering if anyone has ever tested the homemade calibration standard vs. a store-bought standard. When I designed the standard, it was developed using exact values from the scientific literature. It does not depend on a store bought standard (and they were not available to hobbyists at the time anyway), but folks who have compared them find them the same (when made to the weight based recipe). __________________ Randy Holmes-Farley Current Tank Info: 120 mixed reef

11/06/2009, 03:03 PM	#8
Randy Holmes-Farley Reef Chemist Join Date: Apr 2001 Location: Arlington, Massachusetts Posts: 86,233	That sounds good. Let us know how it compares for you. __________________ Randy Holmes-Farley Current Tank Info: 120 mixed reef

11/06/2009, 11:43 AM	#2
Evil Nemo Registered Member Join Date: Jul 2007 Location: Northwest Posts: 84	I've found the accuracey the same in both formulas. Never had a hydrometer for salinity. IMHO they are only good for checking 1966 Dodge truck batteries.

11/06/2009, 01:09 PM	#4
Raggamuffin Registered Member Join Date: Oct 2006 Location: Brandon SD. Posts: 541	I just used dasani to calibrate, ended up being 0.001 off close enough for me Zero'd out with the dasani, tested tank water which 3 of my friends all got 1.025 and came up with 1.026 adjusted and ta da all good.