I am looking for which material to use that would last in swimming pool water? Always underwater and exposed to chemicals and UV. What can you recommend as the correct material that I should be looking at?
White, Strong and Flexible(WSF) is probably your best choice. Note that WSF is porous and will discolour over time, but a UV resisant coating would seal & protect. There's a Nylon chemical resistance chart here, but you might find more specific information by searching for Nylon 12.
Also the Stainless steel material is bronze infused so is quite similar in composition to marine grade stainless and should last indefinitely underwater with zero issues regarding UV.