If you swam for 15 years, up to 4 hours per day, you must have been pretty good!

My sons (16 and 25) both swim, but my 16 year old saw what my 25 year old went through, and decided that was not for him. So, they both swim Masters. They're trying to get back into the routine, which got 'busted' when the 25 year old got married in November. They swam this morning, and both were dead after. Of course, the Master's group in Chattanooga includes some former almost Olympians, so it's a pretty fast bunch.

But . . . the situation in the 70's is the reverse of what you think.

The old pools mostly had 100% outside air on their heating system, whereas in the late 80's newer 'better' pools were built with recirculating dehumidification systems that trapped the volatile chlorinated organics inside the natatorium. My 25 year old was a distance swimmer AND an asthmatic -- his best mile times ALL came on OLD indoor pools. I think his all-time best mile was at the OLD UT-Knoxville pool. He swam there the year before they opened the new one. And, he never had good times in the 'state of the art' Tracy Caulkins pool in Nashville. In fact, we finally gave up on the multi-day championship meets held at that pool. As you know, the distance swims are often scheduled last, and by then the air was so bad he was just wasting the effort.

Regarding Nature2 -- watch out for their recommendations to use MPS. As noted by Waterbear, that stuff DOES trigger reactions in quite a few people.