If the pool is being used, you'll still need doses closer to the 2500 gallon pool than it might seem. A child swimming (or peeing) in a pool consumes the same amount of chlorine, regardless of the gallons in a pool.

In large pools you can store large amounts of chlorine, while having low chlorine levels. In small pools, in order to have enough to 'meet the need' you have to have higher levels.

For example, in a 30K gallon pool, you can store the equivalent of 1 pound of chlorine in a pool (sufficient for several 'pee' episodes), with only 4 ppm of free chlorine (on your test kit). To do the same in a 3,000 gallon pool, would take 40 ppm of free chlorine!