VBA find and replace skipping some cells - excel

Question

I have a bit of code that finds blanks in a given column and replaces them with "BLANK", this has worked fine in the past and works for all of the sheets I am looking at bar one.
In the 'meter' sheet the whole column is blank, yet the find and replace fills all bar 6 of the blanks with no apparent pattern as below. I expect this could be another of my Monday morning 'user malfunction' errors but would appreciate any insight.
I am aware this would be better in a loop, which I will write once I've fixed the problem of it missing some blanks.
Cheers
Public Function FILL_blanks() '''' this searches for blanks
'in the columns in the raw data we are interested in and replaces
'them with BLANK there is a value assigned to BLANK in the flag matrix.
Dim LastRow_g As Long '''' HYDRANT, NODE ---->CHANGES LENGTH FOR EACH ASSET
Dim LastRow_j As Long ''''
Dim LastRow_bp As Long ''''
Dim WS_Count As Integer
Dim i As Integer
WS_Count = ActiveWorkbook.Worksheets.Count
For i = 1 To WS_Count
If ActiveWorkbook.Worksheets(i).Name = "hydrant" Then
Worksheets(i).Select
Range("g4").Select ' this will change j/g/bp only
LastRow_g = Range("g" & Rows.Count).End(xlUp).Row 'define the last row as all of the rows in DMA flag column
Range("r4:r" & LastRow_g).Select
'find and replace below
Selection.Replace What:="", Replacement:="BLANK", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
ReplaceFormat:=False
ElseIf ActiveWorkbook.Worksheets(i).Name = "meter" Then
Worksheets(i).Select
Range("j4").Select
LastRow_j = Range("j" & Rows.Count).End(xlUp).Row 'define the last row
Range("y4:y" & LastRow_j).Select
'find and replace below
Selection.Replace What:="", Replacement:="BLANK", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
ReplaceFormat:=False

Answer 1

I would use Sub here rather than Function because there doesn't seem to be a return. This code replaces blank cells in the columns specified above:
Option Explicit
Sub FillBlanks2() '''' this searches for blanks
Dim LastRow As Long '''' HYDRANT, NODE ---->CHANGES LENGTH FOR EACH ASSET
Dim Sheet As Worksheet
Dim TargetRange As Range
'loop through worksheets in this workbook
For Each Sheet In ThisWorkbook.Worksheets
If Sheet.Name = "hydrant" Then '<~ concerned with col G on hydrant sheet
With Sheet
LastRow = .Range("G" & .Rows.Count).End(xlUp).Row
Set TargetRange = .Range(.Cells(4, 7), .Cells(LastRow, 7))
End With
'apply replacement to the target range
TargetRange.Replace What:="", Replacement:="BLANK", LookAt:=xlWhole, SearchOrder:=xlByRows
ElseIf Sheet.Name = "meter" Then '<~ concerned with col J on hydrant sheet
With Sheet
LastRow = .Range("J" & .Rows.Count).End(xlUp).Row
Set TargetRange = .Range(.Cells(4, 10), .Cells(LastRow, 10))
End With
'apply replacement to the target range
TargetRange.Replace What:="", Replacement:="BLANK", LookAt:=xlWhole, SearchOrder:=xlByRows
End If
Next Sheet
End Sub

Answer 2

I adapted the code from Dan Wagner to account for cells that appear blank but actually have spaces in them. if the cells are only likely to contain a blank or one space then it is possible to use "" and " ".
However, I am sure there is a more elegant solution that accounts for all blank spaces. SpecialCells(xlCellTypeBlanks) is a possibility but it appears to be limited to a certain number of rows.
Sub FILL_blanks() '''' this searches for blanks
Dim LastRow As Long '''' HYDRANT, NODE ---->CHANGES LENGTH FOR EACH ASSET
Dim Sheet As Worksheet
Dim TargetRange As Range
Sheets("Sheet1").Select
LastRow = Range("a" & Rows.Count).End(xlUp).Row
Set TargetRange = Range("b4:b" & LastRow)
'apply replacement to the target range
'"" accounts for true blank cells (no spaces)
' "*" is a wildcard and accounts for one or more spaces
TargetRange.Replace What:="", replacement:="BLANK", LookAt:=xlWhole, SearchOrder:=xlByRows
TargetRange.Replace What:=" ", replacement:="BLANK", LookAt:=xlWhole, SearchOrder:=xlByRows
End Sub
Thanks again for your assistance