BuddyPress.org

Functions.php
Only works with Newest Registered.

// Force Strong Username
function strong_username() {
 global $bp;

 if ( !empty( $_POST['signup_username'] ) )
   if ( !valid_username( $_POST['signup_username'] ) ){
    $bp->signup->errors['signup_username'] = __( 'Your username is too weak or short. Please, use uppercase, lowercase and numbers.', 'bp-strong-username-password', 'buddypress' );
   }
 }
 add_action( 'bp_signup_validate', 'strong_username');

 function valid_username($candidate) {
   $r1='/[A-Z]/';  //Uppercase 
   $r2='/[a-z]/';  //lowercase
   $r3='/[0-9]/';  //numbers

   if(preg_match_all($r1,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r2,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r3,$candidate, $o)<1) return FALSE;
   if(strlen($candidate)<8) return FALSE;

   return TRUE;
}

// Force Strong Password
function strong_validation() {
 global $bp;

 if ( !empty( $_POST['signup_password'] ) )
   if ( !valid_pass( $_POST['signup_password'] ) ){
    $bp->signup->errors['signup_password'] = __( 'Your password is too weak or short. Please, use uppercase, lowercase, numbers and special characters.', 'bp-strong-username-password', 'buddypress' );
   }
 }
 add_action( 'bp_signup_validate', 'strong_validation');

 function valid_pass($candidate) {
   $r1='/[A-Z]/';  //Uppercase
   $r2='/[a-z]/';  //lowercase
   $r3='/[!@#$%^&*()-_=+{};:,?<.>]/';  // whatever you mean by special char
   $r4='/[0-9]/';  //numbers

   if(preg_match_all($r1,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r2,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r3,$candidate, $o)<1) return FALSE;
   if(preg_match_all($r4,$candidate, $o)<1) return FALSE;
   if(strlen($candidate)<10) return FALSE;

   return TRUE;
}