C# Memory Leak on SQL Server data fetch

I have created a simple data fetch method which fetches data from a SQL Server database.

Each time I fetch data by calling this method the memory grows (application pool memory). When I explicitly call GC.Collect() after fetching the data, the memory is half of what it was without GC.Collect().

I know it is bad practice to call GC.Collect(), but without calling I am struggling to reduce memory.

private void DataPopulate(int ID)
{
    using (SqlConnection sqlCon = new System.Data.SqlClient.SqlConnection(ConfigurationManager.ConnectionStrings["SQL"].ConnectionString))
    {
        sqlCon.Open();

        if (sqlCon.State == ConnectionState.Open)
        {
            using (SqlCommand sqlCmd = new System.Data.SqlClient.SqlCommand("engine_connection_sendername_get", sqlCon) { CommandType = CommandType.StoredProcedure })
            {
                sqlCmd.Parameters.Add(new SqlParameter("id", ID));

                using (SqlDataAdapter da = new SqlDataAdapter())
                {
                    using (DataTable dt = new DataTable())
                    {
                        da.SelectCommand = sqlCmd;
                        sqlCmd.CommandTimeout = 300;
                        da.Fill(dt);
                    }
                }
            }
        }

        GC.Collect();
    }
}

I am using the above test method to just check the memory issue. I created a sample .aspx page which only has a button in it . When I click the button this method is called. The Datatable is filled with data from the SQL Server database - that's all.

And I check the memory in application pool. Below is the summary of each time I click the button and the corresponding memory with and without using GC.Collect()

[