SCOM Web Console still display old alerts

Hi,

I have a problem with SCOM 2012 R2 Web console. We decide to use it for monitoring lvl 1 and we did not want to display old alerts in the Active alerts view. We changed the settings AlertsDaysBefore in the web.config file to set it to 1 but we still have some alerts 4 to 60 days old displayed in the WebConsole.

Do you have and idea about this issue?

Thank you for your help !