使用（VAR康恩=新的SqlConnection（_dbconnstr））
{
    // code
}
 

是expaded为：

 的SqlConnection康恩=新的SqlConnection（_dbconnstr）;
尝试
{
    // code
}
最后
{
    conn.Dispose（）;
}
 

所以，你应该处理错误，但你可以忘记关闭连接。

I want to close the SqlConnection in the Finally since the using not really close it and the connection pool gets full. but I don't realize what's the right way to fo that since the conn object isn't reachable any more in the finally section.

try 
{
    using (var conn = new SqlConnection(_dbconnstr)) 
    {
        //...
    }
}
catch (Exception ex)
{
    //...
}
finally 
{
    conn.Close //?!?!?!?!???
}

using (var conn = new SqlConnection(_dbconnstr)) 
{
    //code
}

is expaded to:

SqlConnection conn = new SqlConnection(_dbconnstr);
try
{
    //code
}
finally
{
    conn.Dispose();
}

So you should handle errors but you can forget about closing connection.