The incident happened around 12:30 p.m. at the L.A. Fitness in the 2500 block of Grant Avenue.
All five people were taken to local hospitals by ambulance.
None of the people are in life-threatening condition, medics said.
Officials said it appears there was too much chlorine in the pool.
Investigators remained on the scene Friday afternoon.
The gym is now closed until further notice. Once the chlorine fumes dissipate, the gym will reopen.
