Ability to group dates on 1 pivot without it changing the rest

I have created a dashboard, where it reports different performance figures on a day by day basis.

I want to create a separate tab that shows a week by week summary instead of daily.

To do this I was attempting to group the dates within the pivot to 7 day periods but when I do this is effects all pivots in the document, taking away the daily reporting of my original dashboard.

I also attempted to use WEEKNUM in the original data and report off that instead of the date. But as I am reporting on the financial year not the calendar year, the week numbers do not correspond correctly.

Is there any way that I can report weekly, while also keeping the correct functionality of my daily reporting on the same document?

Any help would be greatly appreciated.

Thanks.