The only thing I use for RAM cleaning is the standard app that came with the phone.
Which app is it? Is this a particular app that came preinstalled or an option in your general settings?
I've been wondering if this is a stock feature but i've been through all of my settings and can't find anything that may result in this.
Yeah, there's a big chance that this floating icon is a stock feature. It's caused by an app or system process that pushes toasts in Dutch (it's Dutch, right?). In how many places have you been able to change the language?
There's an easy way to be sure. Boot your phone into safe mode. If the icon is still there it means that it's a stock feature (or any app that came preinstalled), if not then the culprit is a third party app that you downloaded.
I've never used this particular phone so I'm not sure where to find this feature in the settings. I'll get in touch with the moderators and see if they can move this thread to the P8 forum where it'll be more visible for other owners.
Just a last thought. Have you recently updated any app from the Play Store or received a system update?