Do some observations
To find out what might be causing a rash
after 15-20 minutes in any swimming
pool, one needs to do some observations.
If it's the chlorine, then swimming in a lake won't cause the rash. If it's the cold water, then using a pool of warmer water won't cause the rash. If the body is trying to sweat due to heat generated by swimming, then sitting calmly in the pool shouldn't cause the rash; etc....