Nasa wrote
The reason I was looking at placing lava rock into the basin around the
pump is to provide a place for "good bacteria" to live. In other words I
wanted to create a small bio-filter next to the pump. Since lava rock --
or some other material (like the nylon scrubbers) allow for bacteria to
grown on them -- wouldn't this work?

We did that for several years around our pump.
We cleaned it out once a year and really noticed an improved flow rate on the
waterfall after the yearly cleaning.
Lava rock has lots of little holes in it that tend to get clogged up and are
heavy and hard to clean.
Last year my DH said to heck with this and put the pump back in its slotted
black basket without the lava rock. It was heavy to get out of there and took a
lot of hosing off in a wheel barrel to clean it. So back it went into the pond
last summer without the lava rock.
Early this summer the pump died.
Was it old age? it must have been 7+ years old.
Or was it the fact that it didn't have the lava rock protecting it?
The new pump is back in the pond without lava rock so we'll see next year ;-)

Yes, lava rock will provide biological bug activity going on. Any rock with
water running over it in the pond will do the same. We have rock in our
waterfall, water hyacinths in the upflow stock tank and watercress at the
bottom of our waterfall all doing biological filtering duty along with plants
in the pond.


kathy :-)
algae primer
http://hometown.aol.com/ka30p/myhomepage/garden.html