How Do I Know When It's Time to Change My Pool Filter?

Part of regular pool maintenance is changing your pool filter on time. A new filter will ensure that you are swimming in clean water and you have a good pressure supply of water. But how do you know when it’s time to change your pool filter?
All filters have specified times when they need to be changed. The time will depend on the type of filter your pool system uses. The main types of pool filters are sand, cartridge and grid filters. The general specified times for each are [How Do I Know When It's Time to Change My Pool Filter?]