You're definitely going to need some kind of filtration. The pool filter on it will not work because it is designed to filter chlorinated water. It will clog if your use it for the pond. From the photos it looks like this was never a pond but a swimming pool. Pond filters have to run 24/7 so find high efficient koi pond pumps. There are many available on the market. There are many options as far as filters. You can pick from settlement chambers, barrel filters, bead filters and sumps. I highly recommend a UV on top of a good filter.
Search my pond builds or check out koiphen website.