If the straws are lined up in such a way that the water goes through them,
then you have the internal surface area that you calculated. If they are
put in in such a way that the water does not flow through, then, I think,
the area within the straw would tend to go anaerobic and would serve no
purpose. The Aquaultraviolet tank filter, similar to the bead filters, uses
a hollow media, but it is short chopped pieces so they won't have enough
length to go anaerobic. Find a glue them together, or rubberband them
together and they would be like the pvc pipe, which builds a nice biofilm on
the inside surface.
--
RichToyBox
http://www.geocities.com/richtoybox/pondintro.html


"Matt Rosing" wrote in message
...
Hi,

I want to change my filter media and was thinking about using drinking
straws and was curious as to what people thought. Characteristics of
good filter media a

1) High surface area per volume.

Assuming 12" long straws that are about 1/4" in diameter it takes about
16/in^2 * 144 in^2/ft^2 (=2304 straws) to fill 1 cubic foot. Each straw
has a surface area of 12" * 2 pi r in^2 on both the inside and outside
(=9.4 in^2). Since the straws are against each other say 25% of the
outside surface is lost, so the available surface area of each straw is
1.75 * 9.4 in^2 = 16.5 in^2. This * 2300 straws/ft^3 = 38000 in^2 = 263
ft^2/ft^3 (surface/volume). This is pretty good compared to something
like Springflow which appears to be between 60 and 120 ft^2/ft^3 space,
350 ft^2/ft^3 for lava rock, and 120-250 ft^2/ft^3 for open cell foam.

2) Displaces little water per volume.

Straws don't take much room. Rocks and pea gravel do.

3) Doesn't plug easily.

The inside of a straw can't plug. Possibly the outside could between
the straws but even that is nowhere close to what happens in lava rock.
I've been having problems with pluged filters (lots of algae) and I need
to have something that will go for a week with no problems at all. I
have pea gravel now and I'm having problems keeping the prefilter clean
so the pea gravel doesn't plug.

4) Light weight, easy to work with.

Straws are light. In a filter with straight walls it shouldn't be too
hard to keep them in place.

5) Cheap.

I went to a restaurant supply place on the net and found a case (25000
straws) of 7.75" straws for $42. That would mostly fill my 100 gallon
stock tank.

What do you think?