Randy or Tom-Calibration solution expiration?

[AcroporAddict]

I have a half bottle each of 4.01, 7.00, and 10.01 pH calibration solution by a company called Oakton. They all have an expiration date of 7/2014 on the bottles. Do you think I should stop using them and get new? Sometimes these dates are more of a legal requirement than anything else. Bottles are plastic with screw down caps, and always kept sealed in a dark closet.

Hate to trash them if they really don't go bad. Thank you for any help.

[Randy Holmes-Farley]

The 4 is fine. The 7 is probably OK. Keeping 10 past expiration is risky as CO2 enters it and lowers it.

One thing you can do, which I do, is when you get a new set, measure these old ones. Then, if your meter allows it, you can calibrate with these old fluids such as with a pH 6.95 and 9.8 solution that used to be 7 and 10. :)

I tested fluids and expired fluids here:

A Comparison of pH Calibration Buffers
http://reefkeeping.com/issues/2005-02/rhf/index.htm

[AcroporAddict]

Thanks Randy.

[Randy Holmes-Farley]

You're welcome.

Happy Reefing. :)