help on a Do loop that doesn't work

I have big data file on excel, the file has 6930 rows and 8 columns, the 8 column has percents (0%, 4%, 16%, 18%, 19% and etc..)
I tried to do a macro that paint all the rows that the percent in the end of their row are bigger then 18%, and it doesn't work,
I would like to get some ideas how to make it work, Thanks in advance.

The file start from row 3, so rows 1 and 2 are empty The macro:

Sub Test_4

Dim i As Long

Dim countErr As Long

countErr = 0

i = 2

Do While Cells(i, 1) = ""

If Cells(i, 8).Value > 0.18 And IsNumeric(Cells(i, 8)) Then

Range(Cells(i, 1), Cells(i, 8)).Interior.ColorIndex = 3

countErr = countErr + 1
End If

i = i + 1
Loop

If countErr > 0 Then

Sheets("test").Select

Range("E8").Select

Selection.Interior.ColorIndex = 3

Range("D8").Select

      Selection.FormulaR1C1 = countErr
Else

Sheets("test").Select

Range("E8").Select

Selection.Interior.ColorIndex = 4

Sheets("test").Range("d8") = "0"

End If
End Sub