Swimming pools and spas should always be clean, clear and sparkling. The pump, filter and heater should all be in good working order. Clean the spa cover and make sure the spa is open when the buyer is looking. Take in a water sample to make sure that the chemicals are in balance. This simple task will solve a multitude of problems and the test itself is usually free.
If the bottom of the pool has become yellowed, it should be drained and cleaned with acid. Green water can be treated with chemicals. Scrub the walls and bottom to dislodge algae and dirt which can be taken care of by the filtering system. The pool and surrounding area should be free of clutter, swimming aids, towels and toys. Make sure to repair jets and cracked fixtures. Turn the lights on, especially if the showing is at night.
Since the pool and spa areas are an outward space considered an extension of the living area, it is a good idea to fix broken barbecues and replace outdated patio furniture. Don't think that these things will be overlooked by a buyer just because you have a large pool or spa to focus their attention on. Create an environment that reflects a lifestyle buyers want to envision themselves in, like enjoying barbecues by the pool in the summer with family and friends.