How to make an aquatic plant water filter?

I'm making the kids a wading pool out of a poly water trough. I want to filter the water through a separate trough filled with aquatic plants with probably shale as the base. Not too sure how to set up the filter though. I want to recycle the water through both. I don't want to use chemicals and this will also be a proto-type for a chemical-free swimming pool when they are older. Help please!?

Re-design7 years ago
An aquatic plant filter needs to be about 10 times the area of a high use system.  Plant filters are very slow but self sustaining and chemical free.
Is that climate dependent too ?