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Re: Aquatic Plants Digest V5 #40
Scott H. wrote:
> Allow me to speak purely from naivete -- I invite comments. I have
> always suspected that bioballs where something of a "scam." They
> very little surface area per volume.
Surface area seems to be the stat that the sellers like to quote. It is
just about useless. Take the large surface area in a scintered glass
product for example. That big surface area is mostly lining the pores
inside the medium. The pores are very small and there is little
tendency for water to enter and move through those pores; it only
happens if it's forced. The big surface area around the pores is
useless if there is no flow through the pores. The glass may as well be
solid. Add a biofilm around the outside of the product, maybe
penetrating a millimeter or so into it's porous surface. Now not only
is there no tendency for water to move through the pores,but the water
can't even get to the pores. The pores are all sealed.
You can get a similar effect in biowheels. The big surface area that is
cited for biowheels is created by the surface of all the little fibers
in the fabric. As soon as you get any biofilm on those fibers the space
between the fibers gets filled and most of that surface area is lost.
Biological media, in order to be useful, has to be non-clogging.
Bioballs and similar products don't have nearly as much surface area as
some other products, but a stack bioballs doesn't clog and the surface
area remains useful for colonization.
> But if the idea is to get as much surface as possible into a volume
> while ensuring plenty of air exposure, I can think of lots of things
> better than bioballs and wonder why people buy them for use in
Getting the most surface area/volume is not the idea. The surface area
has to be accessible to flowing water or it's just about useless. The
smaller the open space in the media, the less likely it is to allow free
flow. The best media provides a compromise between surface area and
A biofilter needs to provide surface area, allow free flow past the
surfaces and get enough contact time between the water and the surface
to allow bacteria to do their work. As a result I think it's a fact of
life that an effective biofilter requires a fairly large volume of
I'm sure that out there in the environmental engineering literature
there are formulae for optimizing those factors. There's probably even
a study or two specific to aquaculture.
Incidentally, filter floss is a great mechanical medium. Floss will
provide some biological activity but I wouldn't promote it as a
biological medium. It plugs too quickly and the water flowing through
tends to channel along paths of least resistence. Little of its large
surface area is actually exposed to flowing water at any one time.