Flask Media pH Testing

[Dandrobium]

I was wondering how people test their mother/replate media pH. I have a handheld pH meter that I calibrated and would like to use for this purpose. My question is, for those that use a pH meter, do you dissolve the media in water @ 25degC and test, prior to boiling to dissolve the agar? Also, does the dissolved agar change the pH much at all?

Thanks!

[PaphMadMan]

Agar quality varies, but usually won't have a big effect if the media formula is buffered. So it depends on both agar and media. Unfortunately that isn't very useful.

All components of the media, including agar, would have to be completely dissolved for a meaningful test. That means boil first if you really need to know. And unless you have a fairly sophisticated pH meter and electrode with temperature compensation built in, you will have to let it cool to near room temperature to get an accurate test.

pH meter calibration is not necessarily stable, especially inexpensive ones. I wouldn't rely on it if you can't accurately calibrate on day you use it. Unless I was experimenting with media formulations I would probably confirm that pH is in range with narrow range pH test strips rather than using a pH meter.

[Dandrobium]

Thanks Madman, I'll look into getting some pH strips. I'm just hoping the charcoal in the media doesn't throw off the sample color too much. I'm using some pre-packaged OSP media, but also ordered some from Phytotech, agar included in all of them. P658, P723, & K425.