Pool store metal tests don't mean much. You can do a better test by putting 3 gallons of pool water in each of 2 buckets, and adding a cup of bleach to one, and a 'glug' of muriatic acid to the other. Keep up with which is which. If it's iron, the acid will clear the iron. If it's algae, it may or may not kill the algae. Again, if it's iron, the bleach will tend to make it drop as orange powder. Adding a tablespoon of borax or washing soda makes that even more likely. But if it's algae, bleach will kill it, and let it settle to the bottom as brown or tan -- NOT orange -- powder.

Let them stand -- covered -- for 24 hours, before evaluating.

With a vinyl pool, a 3rd way to rule out algae is to feel the sides: with algae, they will be slick. With iron, they will not. (But, it IS possible to have both at the same time!)

I'd recommend doing the following:

1. Lower your pH to near 7.0
2. Run your filter 24/7.
3. Vacuum & brush the bottom.
4. Do the tests.
5. If it IS iron, get some HEDP & do the metals bucket test on your FILL water.
6. If you can, get some polyquat algicide -- it will help kill algae, and filter out BOTH algae and iron.

BTW, the Culator does NOT look like it's 'working', because the color is all on the OUTSIDE of the bag -- but that may well be because your iron is already in an insoluble form. Lowering the pH and adding HEDP will tend to make the iron soluble again.