When we inherited our pond (from previous homeowner), two 50gal barrels
were full of red lava rock, and the third had a large rolled piece of
filter "batting." We kept the rock through the first year, but it was
too heavy to remove or stir when trying to clean. We refilled the "rock"
barrels with strapping tape (courtesy of the boys' paper route bundles)
which is much easier to stir and rinse out once a year.
--
Kathy B, zookeeper (OR)
3500g pond w/ 13 pond pigs,
2 sun worshipping pharaoh hounds,
and one "koi detective" lhasa apso
("don't bother me now, I gotta
keep an eye on those koi")

BenignVanilla wrote:
What kind of rock is most popular in filters and why?