Hi guys and gals

I am working on my new set-up for the Fire Bellied Toads, the set-up will have a water feature which will cascade down some slate stones. My question is how can I filter the water, because the filters that I have found can't be used as water pumps for features, because they don't have enough power to pump water, and they need to be in water that is too deep (keeping in mind that I will have water for the Fire Bellied Toads at between 2 - 3 inches deep only. If I connect a foam filter sponge just at the end of the water pump is this enough, or is there some other trick that you guys have been using to filter the water.

I will be adding either a fresh water snail or 2 small tetras to help clean up excess waste - which I've used in the past with some great success but I am looking for some alternative options that could work nicely for this sort of setup.

Thank you in advance.