RES water keeps getting stinky shortly after cleaning it

We have a Red eared slider. Every time we change his water, clean his filter, clean the pipes of his filter, less than a week later, his water is cloudy and stinkin' up the place. I keep replacing water and replacing water, but every time I do, the smell goes away for like half a day, then comes back. I end up having to change his water every single day. What is causing this?