I've been working on some FISH/IHC combo stains which have been working well until this last run where I got bright staining on the edge of the tissues but very minimal staining in the middle. The only difference this time was that I used PFA that I had made last week, aliquoted and frozen. I did some reading up on freezing PFA and I know there are mixed reviews. Does anyone have insight on what might have happened? I purchase the 16% PFA ampules so I don't mind making it up fresh every time; I was just trying to save the solution so I don't have to buy it all the time. I don't know what else it could have been. Thanks in advance for any tips!