Water leaches lye from ashes and then that can saponify fat to make soap but I don't think it will happen in the pool. The ashes, as it has been said, can cause pH to go up so you might need to add some acid and physically filter them out. and the best way to get out the fat is skim off what you can and then use an enzyme as Chem Geek suggested. IF there is a problem woith persitant combined chloramnes possibly the use of a strong oxidizer like sodium percarbonate might be in order. If nothing else it can make any debris that has sunk to the bottom rise to the surface for easy skimming.