Any ideas

[fish pond Den]

I'm looking for a pond filter for a 400 gallon fish pond. Does anyone know what a good filter to get for this and should it be above ground or underwater one and I also want some input on this.

I was think I had one of those blow up pool with a small pump I was going to put some small sponges and bio balls in it and see how it works anyone have ideas on this.

 

[Lisak1]

A kiddie pool for a filter?

 

[Meyer Jordan]

I was think I had one of those blow up pool with a small pump I was going to put some small sponges and bio balls in it and see how it works anyone have ideas on this.

Not sure how that would work, if it would even work at all.
Get an appropriate size (one rated for at least a 1,000 gallon pond) above-ground filter. Much easier to maintain than a submerged one.