3 things:

1. Get some polyquat, and add a double dose just before you go. (You can add some now, if you think you have any traces of algae left). Here's the info page: http://pool9.net/polyquat/

2. Read up on borax and muriatic acid. http://pool9.net/borax/ http://pool9.net/ma/ Add 7 boxes of borax and 1.5 gallons of 31% muriatic acid to your pool. That will give you a borate level > 60 ppm. You can add all the borax and a gallon of the muriatic acid at once. Make sure the pump is on and that you can brush / swirl / otherwise dissolve the borax. (Walking around and brushing it, is good). Then add the remaining acid in decreasing doses till your pH is between 7.2 and 7.8.

Borax inhibits algae and remains permanently, unless drained.

3. Put in a clean cartridge before you leave.


Removing phosphates inhibits algae even more strongly, but you don't have time.