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Fresh Fish Freak
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Generally calibration fluids for electronic meters are a set amount (say, the calibration fliud for X brand pH meter is set at 5.25 pH) and then you move a dial or otherwise verify that the meter is giving an accurate reading matched to the known value of the fluid.

REALLY calibrating a meter would involve using several different fluids to test the accuracy along the entire range of measurements. The more that are accurately matched, the more reliable the test results. Most hobbyist-grade meters don't go for that level of accuracy, however.
 

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I understand you use a standard to calibrate an instrument, so I guess what I'm asking is can you use RO or DI water as that standard since it has a known pH of 7.0 instead of having to buy another standard. As you mentioned you can do this for different points in the tools measured range. What I didn't know is if you had to do this at multiple pH's for a controller such as the Milwaukee pH controller.

By the way, I've seen calibration solutions for sale on ebay. Here's a place with free shipping, but i've never used them

http://www.happyherbalist.com/phcalibrationsolutionusewithanymeter.aspx

And looking into this more I found out you cannot used distilled water as the standard because it can give different readings based on different gasses that may be dissolved in it.
 

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I understand you use a standard to calibrate an instrument, so I guess what I'm asking is can you use RO or DI water as that standard since it has a known pH of 7.0 instead of having to buy another standard.

And looking into this more I found out you cannot used distilled water as the standard because it can give different readings based on different gasses that may be dissolved in it.
The same applies to RO and DI water; as CO2 can dissolve into it, the pH will not necessarily be 7.0.
 

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pH buffer calibration solutions

For freshwater planted tanks, you need:
- the pH 7.0 calibration solution only for the Milwaukee SMS 122 pH controller.
- the 4.0 and 7.0 calibration solution for the Pinpoint pH controller.

For African cichlid aquariums or alkaline water, you would use either the 10.0 or the 7.0 and 10.0 calibration solutions depending on which pH meter or controller that you have.

Various manufacturers make 4.0, 7.0 and 10.0 pH buffer calibration solutions for electronic pH meters. (There may be even more pH buffer solutions, but these are the ones that we would ordinarily use.)

You don't have to use the same manufacturers solutions for the same company's pH meters/controllers. You can interchange them. A pH buffer solution of 7.000 from company X should be the same as company Y's.

Normally you see these pH buffer calibration solutions accurate to 2 or 3 decimal places.
- 4.000 http://www.thatpetplace.com/pet/prod/207913/product.web
- 7.000 http://www.thatpetplace.com/pet/prod/207920/product.web
- 10.000 http://www.thatpetplace.com/pet/prod/207923/product.web
 
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