We need to know:
What your filtration is now?
What is the water chemistry?
How long has it been like this?
Is it sticking to the glass?
Have you done (or not done) anything to cause it? (cleaned the filter to well,
changed foods, new gravel/sand etc)?
A diatom filter should clear it up (you may only have to run it for a couple of hours a week depending on whats causing the cloudiness). I wouldn't suggest getting the smallest you can find as you will just have to clean it more.
Dr Joe
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