If it was me I would go by 27 gallons of bleach and throw 9 in today and shock it to get rid of the algae and then have a naeighbor throw 3 gallons in each day you are gone so that it keeps you chlorine up and you won't come back to green pool. When you get back you can balance the pH and alkalinity.

Maybe someone else has a better idea but that's my advice.