Proper pH of fixative and good mounting media is the essential for a good signal to noise ratio. You may want to make up fresh 4% (or less) PFA, which can be stored at 4 degrees Celsius for a week or so.
For a 4% PFA solution follow this protocol.
Add 4 grams of PFA to approximately 70mL of water
Heat up to 60 degrees in a water bath (do not heat any higher)
Add a few drops of 1M NaOH until the PFA goes into solution
Cool to room temperature and add 10mL of 10x PBS.
Adjust the pH to 7.4 and bring final volume up to 100mL
Fix cells for 15-30 minutes, wash away fix with 5 volumes of PBS before putting cells into blocking/permeablization step. Also, make sure your blocking step has glycine in it to properly quench the PFA reaction.
Another option:
This if for tissue culture cells. 1 hour of fixation is overkill in most circumstances I believe. You should have better luck with 15 - 30 minutes of fixation.
Souce: NovoPro 2018-03-15