Very Yellow Media - Can it be fixed? (May/24/2006 )
I know that yellow media generally implies a change in pH (more acidic media). I have been preparing a media from powder Ham's F-12K medium wim 2mM L-glutamine, 1.5 g/L sodium bicarbonate, 10% FBS, and penstrep. The media is quickly (overnight) turning very yellow when placed with the cells (Clone 9 from ATCC). The cells don't appear to be doing poorly, so it doesn't seem to be adversly affecting them. It also doesn't appear to be a contamination problem (however it could be i suppose). However the drastic change in media color from pink to yellow overnight is making me concerned. I'm wondering if something could've been done wrong during the making of the media. It was suggested to me that I put a small amount of NaOH in the media and see if that helps. It didn't seem to do anything. Any suggestions ... or do you think I am going to need to make up a whole new batch of media?
May be u have lots of cells which could make the media change from pink to yellow overnight.
It happpens to me as well, if the cells are confluent.
try with less cells and c if the same happens.
put fresh media on cells or add HEPES pH 7.2
It must've just been too many cells. I split them yesterday and the media hasn't turned to such a bright yellow. However the media is kind of orange. Thanks for the suggestions. 
Just thought I'd confirm what others have said... media that is used-up will turn orange to yellow. If it happens overnight, it's a good sign you've got too many cells in there and they are ready to be split. They are likely so crowded, they won't get enough nutrients.
I think my biggest problem with this cell line was that the person who usually works on it went out of town for several weeks and gave it to me to take care of. I wasn't as used to their growth patterns and she was the one who told me that she thought it was more a problem with the media pH than the cells growing too much. However after splitting the cells ... the media seems to be doing much better. I don't think she was splitting them enough and I wasn't either.