The problem with lava rock is that it is hard to clean.
It is heavy and the muck gets in all those little holes.

When I ran a mechanical/bio filter I used black vinyl
screening, very easy to hose off, light to lift.

Sinc then I have gone to plants only as filters,
water hyaninth in an upflow stock tanks, over
the waterfall planted with watercress. Watercress does
okay here year round in SE WA.

kathy :-)

www.blogfromthebog.com