So--your pond is about the size that I have in my front yard and I actually do not have a filter on it at all. I also don't have any critters living in it, so I don't worry too much about water quality. I occasionally dump and refill water as needed, but that's it. Your water hyacinth and lily's tend to be unhappy with a lot of flow. But--it appears you may have some goldfish in there? So even though you really don't want a submersible filter--you can indeed use any pump you'd like to create a filter. I did that with a pump recently--just surrounded it with aquarium media in bags and then wrapped it in floss. These bags can be used to encase the pump/media/floss: https://smile.amazon.com/TILYO-Drawstring-Biofilters-Filtration-Protection/dp/B08B3F5X7K/ref=sr\_1\_9?crid=3HE44L039P0GM&keywords=submersible+pump+filter+bag&qid=1657108975&sprefix=submersible+pump+filter%2Caps%2C52&sr=8-9

A much easier alternative would be to just purchase a submersible aquarium filter (example: https://smile.amazon.com/FREESEA-Internal-Aquarium-Power-Filter/dp/B08PCKRLMD/ref=sr\_1\_9?crid=2FWPMUSH9GP1J&keywords=submersible+aquarium+filter&qid=1657108794&sprefix=submersible+aquarium+filter%2Caps%2C57&sr=8-9)

If you are still wanting an external filter, this may be an option too: https://webbsonline.com/Category/Aquascape-Pond-Filter-Urn You will still need a pump by the way. I have seen folks construct their own external filters that blend into the spot that they have so it isn't so obvious. Any vessel can be turned into an external filter with enough plumbing knowledge and patience (https://www.youtube.com/watch?v=cIjY0U6BCVc).

Along those same lines--how about a bog filter? Quick google and you will have a lot of videos explaining how to construct one.