Use product options to display filter list in category. This module automatically generate the filter list using the product options available for the opened category. Stop add/edit opencart filter for every products and categories manually. You have just to insert option and activate the module to be displayed in category layout.
1. Install from the extension installer the downloaded package
2. Go to "Extension", select "Module", and Install and Enable the "Filter Products with Options"
3. Go to "Design">"Layout", edit "Category" and add in the "Column Left" the installed module "Filter Products with Options"