Re: Wet/Dry, Trickle media

["James Purchase" <jppurchase at rogers_com>]

Adam Shaw wrote:
"I'm thinking of going that way instead of using the typical bio-ball
plastic setup, and wondering if anyone else has tried it. It's quiet
expensive stuff (Matrix is).. Seems that to fill a trickle filter
biotower would cost quite a few hundred $$ whereas the bio-balls that I
can get will cost around $55.."

Go to Seachem's website and read what it says about Matrix. Then go to the
Dupla website and read what they have to say about their Biocascades and
Minicascades. I realize that for $55.00 the bioballs you are considering
aren't made by Dupla but Dupla is the only company that has much which is
useful to say about the effective use of such things. And for this
comparison, one ball is pretty much like another.

Your trickle filter sounds like it was designed and sized to accommodate
ball type media (bioballs, shotgun wadding, etc.). These are designed to
provide exterior surface area in a format which will resist clogging and
channeling of the water flowing through it. The better the design of the
bioball, the more surface area and flow-thru it offers.

I have owned and used several types of bioballs over the years, and the
Dupla Biocascades and Minicascades seem to be well worth the money they want
for them (but that's only my opinion). Buy them once, they last forever....
you soon forget how expensive they were in the first place...or, at least, I
have forgotten...

With any bioball, the available surface area is ALL on the outside.
According to Spotte, these things are designed to allow for the formation of
a biofilm on the exterior surface of the ball. The "filtration" of your
water takes place inside the biofilm, courtesy of the bacteria which create
the film. Due to the high oxygen environment created by the "trickle tower",
the bacteria which populate these things are aerobic. They live for a few
days, do their thing with NH3/NH4 and NO2, multiply like crazy and as the
biofilm thickens, the lower layers of bacteria die (from lack of oxygen).
The biofilm then "sloughs off" the substrate (the bioball) and is soon
replaced by freshly replicated bacteria from the surrounding areas. Its self
cleaning and pretty much self maintaining. But it does require a certain
volume in order to provide sufficient surface area to support the mass of
bacteria needed to handle the ammonia produced by the fish in your tank.
They are also considered to be nitrate factories because, if well designed,
they are very efficient at converting ammonia to nitrite and then nitrate.

Matrix offers both surface area AND internal pore space, much greater than
ANY bioball. But it does this at the expense of the voids which help prevent
clogging and channeling (water will seek the path of least resistance on its
way through the unit). Seachem recommends the use of Pond Matrix for drip
tray applications (trickle filters/wet dry filters), most likely to maximize
the flow thru characteristics and prevent clogging. With either size of
Matrix, it is probably very important that the water be mechanically
filtered first - you don't want detritus to get into it and clog up the void
spaces between the particles.

This need for mechanical "pre-filtering" is probably not as essential for a
unit using bioballs as the void spaces are much larger and most detritus
would pass right through the balls.

With Matrix (or with Pond Matrix), the design of the drip tray would
probably also be more important - you want to ensure that the flow of water
is evenly distributed so that it gets into contact with the whole body of
the media.

The internal pore space of Matrix and Pond Matrix is designed to support the
formation and growth of bacteria which don't need oxygen (anaerobic) and
which have the neat trick of consuming nitrate and turning it into nitrogen
gas (NO3 -> NO2 -> N2) which gets released into the atmosphere (and out of
your system). That is the theory. In practice, if conditions are not
optimal, the conversion process can stall at NO3 -> NO2, and the nitrite can
cause problems in your aquarium. The "denitrification" process also takes
much longer than the "nitrification" process, meaning that the "dwell time",
for water in the system must be longer in order to accomplish the conversion
completely. How well this works is going to depend on the design of your
filter and upon how well maintained it is.

The volume (physical space) needed to hold the amount of Matrix or Pond
Matrix necessary to process the same amount of water would most likely be a
lot less than the volume needed to hold the equivalent amount of bioballs.
Its a trade-off between surface area and void space. In the unit you have,
it sounds like you have the space (for bioballs). It sounds like you have
way more space than you would need if you used Matrix. It probably wouldn't
be necessary to fill all of the available space with Matrix (or, if you did,
it could handle a MUCH bigger tank). Just make sure that the design of the
unit allows for prefiltering the water BEFORE it flows over the Matrix and
it is capable of distributing the water evenly over the whole volume of
Matrix.

Then we turn to the real need, in a well planted, lightly to moderately
stocked aquarium for auxiliary "biofiltration" in the first place. Do you
NEED to do this in your tank? Bacteria capable of converting NH3/NH4 into
NO2 and then into NO3 exist on every internal surface of your aquarium
(glass, gravel, plants, driftwood). Given a healthy amount of internal
circulation (power head to move the water around), these bacteria can handle
the waste load from a few fish with no problems. If the aquarium is heavily
planted (that IS the type of tanks we are supposedly maintaining and talking
about here), the plants themselves get into the act, sucking up the NH3/NH4
before the bacteria get a chance to, thus subverting the "nitrogen cycle"
and rendering it moot. Plants can use either ammonia or nitrate as a
nitrogen source, (the preference is species specific but that's really
beside the point).

A well planted, moderately stocked aquarium doesn't usually NEED an
auxiliary biological filter. It might benefit greatly from mechanical
filtration (to remove particulate matter) but the plants themselves can deal
with the waste products from a few fish. If you want to pack the fish in
like sardines, or you are keeping big, massive fish, an auxiliary biofilter
can add an extra measure of insurance.

External wet/dry filters offer a convenient place to put equipment that you
don't want visibly in your tank. But their biofiltration function was
initially designed with "fish tanks" in mind, not with "plant tanks". What
kind of tank do you have or do you want to have?

James Purchase
Toronto