Change to Secure File Delete

Having just bought the Pro Version can't seem to change my settings;

CCleaner shows secure deletion is set at "Normal" (Faster)...

I have tried to click the change this to "Secure" (Slower), but this feature and the overwrite preference box is greyed out and currently shows complex overwrite 35 passes, as per the screen shot...

Does anyone know how to change this over to secure, please??

Thanks in advance

Screen Shot 2018-06-24 at 08.21.10.png

Oh, forgot to state my Mac uses 500gb of flash memory, should this make a difference t possible settings??

Many thanks

not having a Mac, but I would guess it's due to you having a solid state drive.

using secure wiping on a PC with CC pops up a big warning flag.

mta made a great guess. Don't know when it started, but El Capitan is the first OS I know of that denies use of Secure Erasing.

I do wish Piriform, Apple and other developers would make it an option for all the people that use HDDs. We have to find third party applications that will perform this action.

Do like mta says happens on PCs with a big warning. Not a big fan of SSDs. Waiting for the next great recording medium.