VBA loops

I really have no idea what that means. If you want simply to take bottom from top for each cell, then this does that:

Sub AquiferCalc()

Dim lLR As Long
Application.ScreenUpdating = False
With Sheets("Top")
    lLR = .Range("A" & .Rows.Count).End(xlUp).Row
End With
With Sheets("New Bottom")
    .Range("A1:IV" & lLR).FormulaR1C1 = _
        "=Top!RC-Bottom!RC"
End With
Application.ScreenUpdating = True

End Sub

Regards, TMS