Whenever a pool is drained, you will want to raise the Chlorine Stabilizer, or Isocyanuric Acid, to 100 ppm. for most play pools, around 15,000 gallons, this requires about 10 lbs. or so. For most diving pools of 23,000 gallons, you will need about 15 lbs. or so. I add it directly to the pool, scattering it across the floor to lighten up any staining. (Yes, fairly even dispersal is important, if this is your goal. You can also, after backwashing or cleaning you filter, temporarily remove your pump basket and your skimmer basket and float valve, and add it directly to the filter via the skimmer.
            I always add about 2 lbs. of shock (If the temperature is above 80 degrees) or a gallon of bleach, if it is below that outside, fill up the chlorinator with tabs, and sometimes add a bottle of "Stain Treat" or other stain inhibitor, as well.