C# - Counting checkboxes that are selected not working

So first I'm getting everything from the database and adding a checkbox for each line of new data, this is all working:

while (reader.Read()) {
                    idtema = "";
                    nome = "";
                    filename[i] = "";

                    TableRow rows = new TableRow();
                    TableCell cell1 = new TableCell();
                    TableCell cell2 = new TableCell();
                    TableCell cell3 = new TableCell();
                    TableCell cell4 = new TableCell();
                    CheckBox ch = new CheckBox();

                    idtema = reader["IDTema"].ToString();
                    nome = reader["NomeArtista"].ToString();
                    filename[i] = reader["FileNameTrabalho"].ToString();

                    cell1.Text = idtema;
                    cell2.Text = nome;
                    cell3.Text = string.Format("<a href='/Tema" + idtema + "/" + filename[i] + "' data-lightbox='images1'><img height='100%' src = '/Tema" + idtema + "/" + filename[i] + "'>");
                    cell4.Controls.Add(ch);

                    rows.Cells.Add(cell1);
                    rows.Cells.Add(cell2);
                    rows.Cells.Add(cell3);
                    rows.Cells.Add(cell4);

                    TabelaPrincipal.Rows.Add(rows);
                    Button1.Visible = true;
                    i = i + 1;
                }
                con.Close();

After this I check my 4 checkboxes and I press the button to read the data:

public void Button1_Click(object sender, EventArgs e)
    {
        int check = 0;

        foreach (Control item in this.TabelaPrincipal.Controls)
        {
            if((item is CheckBox) && ((CheckBox) item).Checked)
            {
                TabelaPrincipal.Visible = false;
                Button1.Visible = false;
                DropArtista.Visible = false;
                DropEscola.Visible = false;
                DropConcelho.Visible = false;
            }
            else
            {
                check += 1;
                Response.Write(check);
            }
        }
    }

The response.write comes back "1" and that's it (not even checking if its selected), how do I change so it reads all my checkboxes and the collumns?