Remove FFs works, you just used a value that is too high for the scene. Keeping it at 5 is the best. Please note that if you have FFs still in the scene then it's a matter of light/material combination. You need to change your materials to remove those last FFs.

Please also note that render noise is not to be confused with FFs. I noteicd that many people are confused about what FFs are. Render noise is not FFs and the control in Reality will not solve the issue. With some materials you migh get into a situation where the render noise doesn't get resolved. In that case you have to act on the materials and lights.

FFs are large specks of white pixels that get worse and worse as the scene renders. They are fairly rare to obtain.

 

Hope this helps 

Paolo

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