Now, I’m trying to get this damn filter clean.. I tried to use a dust brush, then some lense tissue with a cleaner, and there are still fine speck.
How old is your daughter.. is she teething? If she bit down, she could damage the filters coating.
I have tried cleaners and found that they all seem to leave a little bit of a film (bright light at an angle, bouncing the light at an orientation with equal incident and reflective light reveals the film). Distilled water is better, the best that I have found is reverse osmosis water (which is what integrated circuit manufactures use to clean things with). I tend to use cotton swabs (no paper – paper can be harder than some coatings). I rinse by dribbling the reverse osmosis water at an angle so it runs off the filter, using the surface tension of the water to ‘dry’ the filter. There is a small amount at the bottom corner afterwords, which I pick up with a dry cotton swab. I don’t immediately put the filter on afterwords.. I put the filter in a safe non dusty place to dry for a few hours.
