Try mixing the pool water and reagent first, and let it sit 2-3 minutes before testing again, and see if that makes a difference. Honestly, if you are losing that much over a week's period of time and can't account for it with dilution, you might start investigating a possible leak.

If you have algae starting in the pool, you need to shock the pool and maintain that shock level until the algae is gone. Vacuuming and backwashing may get rid of what you can see, but it won't get rid of the algae that's still in the pool that is too small to be visible.

Janet