Filter water taste muddy

[upup]

So I got a reverse osmosis water filter. The water started to taste muddy. I went to the shop and got replacements for filter number 1 and 3. Both were dark brown when I remove the old ones. So I replace them and the water tasted good again. After 3 days the water started to taste muddy again. The system is about a year old, nothing has ever been replace.

Could you give me advise please.