Changing Ranges in VBA

[smurray444]

Dear all,

I have written the following code which replaces "" (a blank) with a zero, yet it applies to the whole workbook. How would I change this to apply it to the active sheet of range A1 to J815209?

Sub ReplaceCharacter()
For Each mySheet In ThisWorkbook.Worksheets
mySheet.Cells.Replace What:="", Replacement:=0, LookAt:=xlPart, SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, ReplaceFormat:=False
Next
End Sub

Thanks
smurray444