Weird Blue Stuff in Sand Filter

We recently bought a house with an in-ground vinyl pool. Been working on getting the levels right for a few weeks, but this afternoon after adding about 8 lbs. of borax (pH is currently < 7), I noticed some cloudiness in the water. After doing some research here on the sand filter and seeing Smykowski's tutorial on deep cleaning, I decided to open up the filter and see what I could see.

The previous...

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