Mix your bleach -- 1 gallon to a couple of gallons of water -- and add it NOW! Do NOT wait for the pump to be installed. You can pour bleach into the pool, walking it around the edges, and get pretty fair distribution. But do not let it turn into a slime pit while you're working on the pump. It's much, much easier to maintain it, now, than it will be to clean it up once it becomes a swamp.

Ben