Your pond should be built based on what you want in it. If you just want some goldfish, you can likely drop a canister filter in there and a pump and do fine- they need almost nothing. If you instead decide to go with Koi, you're changing the game because they need a lot more filtration because they are messy and grow really fast (but are beautiful!). If you are going to make it a bog-like pond with a ton of plants, then you will get the big benefit of a lot of extra bio-filters in the plant roots and they'll even "establish" your pond over a year or so with beneficial bacteria, a complete eco-system!
Here's my pond. I love my chickens, but fish are so much more calming, for sure! When I want to smile and laugh I go watch chickens. When I want to rest and be calm, 100% at the pond.
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