Inflatable pools used to be limited to the kind of "kiddie pools" you could easily blow up with a small hand pump, or even by mouth in a pinch. These pools held maybe 30 gallons or so, and it was a simple matter to empty them out every day and just fill them up again with fresh water each time you wanted to take a dip. Now inflatable pools, or the "easy set" type with an inflatable ring and vinyl sides, can hold hundreds or even thousands of gallons (up to 6,000 gallons for a pool with 4-foot walls and 18-feet in diameter). With a pool of this size, you certainly don't want to fill it on an as-needed basis. Instead, it's far easier to find ways to keep the water clean.
Purchase commercially-manufactured pool chemicals, including test strips to check your pool's chlorine and ph levels, chlorine and a stabilizer/conditioner to protect your pool from sunlight. Certain manufacturers are now coming out with pool chemicals designed specifically for above-ground pools, including the vinyl-sided, inflatable ring type.
Shock your pool with a large dose of chlorine once a week. You can purchase special pool shock treatments in the form of chlorine granules, which are to be mixed with water and then poured into your inflatable pool. With inflatable pools, it is important to make sure that no undissolved chlorine granules settle to the bottom of the pool, as these may harm the liner.
Try a homemade shock treatment using chlorine bleach with the same type of liquid bleach you use for laundry. Measure out 2 1/2 tsp. of bleach for every 100 gallons of water your pool holds (or 1/4 tsp. for every 10 gallons, if you have a smaller inflatable pool). Then add the bleach to a bucket of water. Pour the water into your pool, mixing to make sure all of the pool water gets chlorinated.
Keep debris out of your pool by covering it when it is not in use. Covers are available for inflatable pools ranging from 8 to 24 feet in diameter.
Drain your pool periodically. Drain it daily, if it is small enough to permit this, or weekly if it is mid-sized. But try to drain even the largest inflatable pool at least once a month, as no amount of chemicals can clean the water of all of the dead skin cells, bugs, leaves, or just plan dirt that will accumulate there. When your pool is drained, you may scrub it out with mild detergent and a soft scrub brush to clean any scum or buildup off the pool walls.