Yes!

If you aren't careful, and there is still copper in the water, you can stain your pool. (Of course, it may already be stained!)

1. Get a K-2006 test kit (info link in my signature)

2. If the owner left a copper test kit, use it, and check copper levels.
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3. Order some polyquat algaecide - 1 qt per 10K gallons (can possibly find it locally, but Amazon has it at a good price)
Kem-Tek 60% polyquat
Getting Amazon Prime will let you ship it fast and free -- but remember to cancel Prime if you don't want to keep it. (I end up depending on it at Xmas!)
Amazon Prime
4. Find out pool info: gallons, size, pump/filter make/model, and post that info here.