Planter pot tank?

[V p1839]

So I had this idea this past summer to turn a rather larger round planter pot into a tank for my koi fish.

The only issue that I am having is how to filter it. Is there a way I can create a filter or cut a hole to create an overflow?

Any ideas would be a great help.
Thanks

 

[GodFan]

I would think it wouldnt be big enough... But I cant see it so I will trust you
Could you not run some pvc for like a canister filter to it? You could hide i with a neat shelf with plants on it.