What precautions should be taken before draining a pool for cleaning?
After seeing several pools come 1-3 feet out of the ground and close to 10 have there bottoms heaved up and broken I would never drain a pool in the winter (Northern California) You may be able to drain 1/3 of the pool and add fresh water I use the vacuum and pump it out of the pool this way you are making use of the water not just dumping. Then hit it hard with a shock treatment 2x or 3x the normal amount. Make sure to backwash your filter 1-2 times a day. I used to use 1-2 gallons of liquid chlorine with the shock treatment it just seams to work better. Also a clarifying agent like clear blue or aqua blue will help. I have cleaned pools in the past that were black with several inches is silt on the bottom. If you do use your vacuum to dump the water make sure to check the pump strainer basket and remove leaves and twigs that are picked up off the bottom.