I assume you have already thought of this so please forgive 'the reminder'.. Considering that you are literally 'building over a hole' (swimming pool), just know that unless you put a sump pump or something to 'get rid of the buildup of snow, ice and water that will have fallen down between the deck boards(with every snowfall, rain water etc).. the 'water' below the deck will destroy the footings (erosion around the footing) and be a great breeding ground for mold and mildew in the spring and summer.