Edited to add: To clarify what I'm optimizing: I want to minimize the time it takes to get the pool water from some initial temperature to some higher desired temperature.
That suggests there are general principles at work here.
To move forward, a force must be applied to help the body accelerate from rest in a certain direction.
But if you want to become a faster, more agile swimmer, it may be time to start taking a closer look at physics.
Therefore the boiler works harder when more heat is being transferred to the pool water more heat transfer implies colder return to the boiler implies more work for the boiler to reheat that water.
If I slow the flow, it will start getting hot again.
Many apologies for not having provided this possibly key bit of information in the first place.
But if you take that distance traveled and divide it by time, you get the swimmer's velocity.