I have anAutostart 500 fish tank with a Fluval filter The tank contains 2 large goldfish 4 small catfish and 2 loach. I have had the tank and filter for nearly three years Everything is cleaned regularly and the water is changed in stages regularly.
THE PROBLEM. In the last three weeks every two days the water is cloudy. When I check the filter it is filthy each time. I use goldfish flakes and catfish pellets for food. Don't know what to do to solve the problem. Both of the foods being used are king British so it is not cheap food. Anybody ant ideas

You may be overfeeding them. The uneaten food rots and causes bacterial bloom, and it would also explain why there's so much detritus in your filter.

You need to do a 25-30% water change and feed them a bit less. And test the water quality (PH, nitrites, nitrates and ammonia), because low quality can often be a cause of cloudy water. This article explains more:

http://www.ratemyfishtank.com/articles/187

As above plus maybe get an extra or a more powerful filter in there . I have two filters in my tanks just in case one fails for for some reason . Goldfish and catfish are all heavy feeders and therefor produce an awful lot of waste .

Goldfish are really pond fish of course !!