Have you shocked your pool up to and FC of 15ppm and kept it there until the algae is gone, and then for another 24 hours? All you need is bleach or Liquid Chlorine (LC) to do it. 3 gallons of 6% should do it to add roughly 10ppm to your pool.
And what are you testing it with?--the 5.5-7 sounds like a strip.
Carl
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