How to keep ducks out of the outdoor pool?

here are some ideas

https://www.youtube.com/watch?v=GQqFHZZwz-w

https://www.youtube.com/watch?v=HqE3ao1FzzA

1) Remove anything that might attract birds to your yard, such as a bird feeder or a bird bath. Take away all flowers or plants that might lure birds into your garden.

2) Buy a fake replica of a predator to scare the birds away. Most people opt for owls, which can be placed in or hung from a nearby tree or awning. Some birds might respond better to rubber snakes or alligators placed around the perimeter of the pool.

3) Keep the birds away by moving the predators every few days. Some pool owners think it is easier to buy a mechanical replica that detects motion. For example, some owl replicas will flap their wings or move their heads when they sense movement in your yard.

4) Place a toy or object in the water when the pool is not covered. Some pool owners have used an inflatable dolphin will keep birds out of your swimming pool area.

5) Choose a holographic product for a more aesthetically pleasing alternative, such as such as Irri-Tape. The combination of the movement and the light reflecting from the water surface will keep birds out of your swimming pool. Alternatively, some people like a product called Terror Eyes, which is a balloon with holographic eyes.

I know you said there are no dogs. But maybe you could get a bluetooth speaker near the pool with dog barking sounds coming from it.

Keep certain inflatable animal toys—alligators, killer whales, snakes, and dolphins—in the pool when you're not using them to scare off ducks.

We get ducks every year. Now they only show up when the pool cover is on...because when the pool is open there's so much activity they're scared and leave. We didn't have to go in it every day, but when we saw them, we would go out and kick and splash. After a few days of this activity, they realized it was not a safe place for them and left for calmer water.

Add a few plastic hawks and owls. Move them around. Plastic snakes as well. Works on other birds.

Keep the pool covered unless you are in it, is my best advice.

1. Put Out Some Animal Pool Toys When You're Not Around.
2. Invest in a Solar Cover.
3. Own a Dog.
4. Install an Automatic Pool Cleaner.
5. Put up Fishing Line.
6. Buy Duck Off.
7. Use a Motion-Activated Sprinkler.
8. Use Bird Netting.

https://poolcareguy.com/how-to-keep-ducks-out-of-pool/ this resource may help you out.