When you use a PHP framework like Codeigniter to speed up web development, it is a good idea to beware of its strengths and weaknesses.
The strengths for using the framework are its built in classes and security checking. This takes place when a controller calls view files and outputs the data. One such file, Input.php is located in the libraries folder. This file will do checks with the cookie and input data. If your view file was made in pure php, the characters and coding could create an issue.
The file, Input.php does cookie and input data checks. If your view file was made in pure php, the characters and coding could create an issue. In this case, recoding a php/mysql application to be a Codeigniter application could take more time than desired.
Since some available scripts may require time to recode for Codeigniter, a faster option would be to dump the php application inside the root folder where the system folder is located. Now, the php/mysql application can be used without any influence from Codeigniter; even though it still has access to the css file and it can use the same database as the Codeigniter installation.