I don't have any experience with animal pools
however, I have read a cdc report that stated lots of problems can occur with chlorine pumps... they must be monitored daily & frequently during the day.

some otters do live in saltwater, could a salt-water-generator be more effective ( I wonder) ?

From observation of a otter tank near by,
I see that they have at least three of four skimmers in their free-form pool.
each skimmer has skimmer blockers ( or protectors) as the otters are constantly sticking thier paws in. One otter kept trying to put things in it ( lol)
I would also suggest a mani-drain protective cover for safety

Please post pictures of the otters in pool when completed
( I love otters )