cleaning posts

I’m creating custom pages, not from a template, but just using WP to allow the customer to make text changes. When I go to display a single post, it gives me all kinds of strange characters. For example, a space bar comes out as ?. Is there a default WP function to call that will clean this up? I’ve searched high and low, and I guess I do not know the correct wording for this problem.

Here’s what I am currently using:

<?php
   $post_id = 19;
   $queried_post = get_post($post_id);
   $content = $queried_post->post_content;
   $content = apply_filters('the_content', $content);
   $content = str_replace(']]>', ']]>', $content);
   echo $content;
?>

Any help greatly appreciated.