How much water changes should I do on a pond

[Benji k]

I have ribbon grass, elephant ears ,papyrus (have to be careful it doesn't take over) and bacopa for the floating plant. And some water lilies in one pond. I also have one that is just a large pot, prob not over 20 litres ..5 gallons. That has one plant in it that likes shade as it is on my verandah. I've never fussed with any of them after set up.

What fish do you have in 5 gal