Skunky, do you live where there are lava rocks outside? If so then yes. I have reused these rocks a few times. The first time I washed them, there is some sediment that comes from the rocks. So if you get them from outside, rinse them off the first time. The lava rocks work because you're creating a porous surface for the good bacteria to live in. Ponds are kept clean with filters and the filters can be made of anything plastic or nylon. I saw pictures of a pond filter made with a large bucket filled with green kitchen scrubbies. Next time you're at Home Depot look at the pond stuff.

On overgrow, someone threw algae into his system, just to prove that the beneficial bacteria would take care of the algae. It did.