The Problem
Every tank needs regular cleaning and maintenance, but your filter media should stay fairly clean for weeks or months at a time. If you notice reduced water flow and are having to clean your filter media between water changes, it may indicate an underlying issue that needs your attention.
Treatment & Prevention 
Below are some common reasons for excessive clogging in your filter media, and how to address them:
- Algae: Some algae in your tank is fine, but it can be a problem if it is clogging up your filter media. Reducing nitrate levels in your tank can help by depriving algae of a needed nutrient. This can be achieved by doing water changes more often, adding plants that consume nitrate, or introducing materials like live rock or certain types of biofilter media that house anaerobic bacteria that break down nitrates.
- Overfeeding: Excess food can quickly accumulate in filter media, leading to clogs, and as well as releasing toxic ammonia as it breaks down. As a general rule, you should only feed what the fish can consume within 4 or 5 minutes, removing anything left over after that time. You may also want to feed smaller amounts on a more frequent schedule.
- Filter media: Biological filter media is designed to have lots of surface area to house the largest possible population of beneficial bacteria. But sometimes all those tiny openings can mean debris can easily get trapped. For better performance and less maintenance, consider adding mechanical filtration to remove larger debris ahead of your biofilter, or trying a different biofilter media with better flow capabilities.
Addressing these types of issues can help to prevent clogs in your aquarium filter, so you can spend more time enjoying your tank and less time maintaining it.