manipulate part of array before saving

I’ve set up Custom Fields that accept a URL to a social media site, I would like to then check and see if the field contains http:// and if it does not, add it before saving to the db.

// Add Social Media Meta Boxes
function add_social_box()
{
    add_meta_box( 'social-media',
            __( 'Social Media'), 'social_meta_box_callback', 'page', 'advanced', 'high');

}
add_action( 'add_meta_boxes', 'add_social_box' );

function social_meta_box_callback( $post ) {

    // Add a nonce field so we can check for it later.
    wp_nonce_field( 'social_save', 'social_meta_box_nonce' ); ?>

    <div id="meta-inner">


    <?php 
    /*
     * Use get_post_meta() to retrieve an existing value
     * from the database and use the value for the form.
     */
    $accounts = get_post_meta( $post->ID, 'accounts', true);
    // foreach ($accounts as $account) {
    //      $parsed = parse_url($account);
    //  if (empty($parsed['scheme'])) {
    //      $account = 'http://' . ltrim($account, '/');
    //  }
    //  var_dump($account);
    // }    
    ?>
        <div>
            <label for="facebook">Facebook</label>
            <input type="text" id="facebook" name="accounts[facebook]" value="<?php echo esc_attr( $accounts["facebook"] ) ?>" />
        </div>
        <div>   
            <label for="twitter">Twitter</label>
            <input type="text" id="twitter" name="accounts[twitter]" value="<?php echo esc_attr( $accounts["twitter"] ) ?>" />
        </div>
    </div>
<?php }

When I var_dump($account)it gives me the correctly adjusted urls here.

function social_save_postdata( $post_id ) {
    // verify if this is an auto save routine. 
    // If it is our form has not been submitted, so we dont want to do anything
    // if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) 
    //     return;

    // verify this came from the our screen and with proper authorization,
    // because save_post can be triggered at other times
    // if ( !isset( $_POST['menu_meta_box_nonce'] ) )
    //     return;

    // if ( !wp_verify_nonce( $_POST['social_meta_box_nonce'], 'social_save' ) )
    //     return;
    $accounts = $_POST["accounts"];
    foreach ($accounts as $account) {
        $parsed = parse_url($account);
        if (empty($parsed['scheme'])) {
            $account = 'http://' . ltrim($account, '/');
        }
        update_post_meta($post_id,'accounts',$accounts);
    }   
}
add_action( 'save_post', 'social_save_postdata' );

And using the same logic that works in the callback function above, this does not save the adjusted url in the db. My guess is that the data structure that I retrieve from $_POST["accounts"] is not the same as the serialized data I fetch from the callback function. Unfortunately I am not sure how to get a look at that data to determine the correct structure to parse the URL.