40,000 gallon units typically are BARELY big enough for 40,000 gallons . . . and 5% of 40,000 gallons is 2,000 gallons.

But . . . suit yourself.

I have no idea what your load, indoors, will be.

Outdoor load tends to depend on sunlight, unless bather load is at commercial levels. Indoor pool load is based on bather load. If your pool is unused, almost any SWCG will be too big, so you'll need a time clock on the power input. If the pool is used regularly for laps by a real swimmer, bather load (sweat + skin), bather load may be MORE than a typical outdoor pool, used only for intermittent recreation. If the pool is used by a former competitive swimmer, who pees in the pool (it's not just Micheal Phelps and Ryan Lochte -- virtually all serious USS swimmers do!), then the effective bather load is even higher. Ditto for a pool used by babies, or the Depends crowd.