Welcome to TFP!!
Can we get a full set of water test #s, please?
Where are you located? (there are bio-films that appear purple/pink in certain areas of the country)
The reason I ask for this is that your film wipes off easily, which leads me to think "bio-film"
Please answer my questions, so we can give a proper diagnosis

(and it won't hurt to up your sanitizer in the meantime

)