As John noted, if there's cloudiness from algae growth then it's a difficult situation. The longer you wait to deal with it, the longer the algae has to grow in a pool with no chlorine and full of ammonia (nitrogen source) nutrient. The ammonia taken in by the algae is going to need chlorine to oxidize, but be more difficult (slower) to get rid of when it's part of algae which converts a lot of the carbonates in the pool into organics.teapot said:
I suppose if you had some way of very quickly removing water and then hit the remaining part with chlorine and refilling, then that would be OK, but you'd have to work fairly fast and not take days for the process. Also, though chlorine isn't free, neither is water in large volumes. Of course, the best way to deal with this is with prevention and not letting the chlorine get too low (especially near zero) in the first place.