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Archive-name: aquaria/general-faq/filters
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				  Filters

Rev 1.23 9/3/94

Prologue:
---------
This monthly series is intended to address some of the frequently
asked questions (FAQ) on the rec., alt., and sci.aquaria newsgroups.
Because the answers may not be complete, please feel free to ask
questions.  This is only intended to address first level concerns, and
not to dampen discussions.  Please see the file README for pointers to
other topics.

Please review and send any corrections or inputs to the FAQ maintainers
with "(FAQ)" in the subject line.  You are absolutely welcomed to tackle
(i.e. WRITE) sections that have not been written yet.

I've received recommendations to put email address "pointers" in
the FAQ to vector questions to specific experts on particular
subjects.  If you would like to offer yourself as such an expert,
please send me your email address and the specific topics you want
to host.  Please include an email path that is generally accessible
to the greatest number of people.

FILTERS AND RELATED QUESTIONS:
------------------------------
     Filtration is very important to the welfare of your guests,
and as such there are many different kinds of filters.  Since there
are many brands and opinions, one should post requests for
recommendations.  Equipment that is typically found on advanced
aquarists' systems are also noted.  These are typically more
expensive, and are generally not needed by, nor recommended for
beginners.
     In general, if one needs to rinse/wash filter media, one
should never use soap or hot water (or for that matter, very cold
water).  This would serve to kill the beneficial bacterial colonies
in the filter media.  (See nitrogen cycle).  Use the reject water
siphoned out your aquarium to wash/rinse filter media.
     The following filter discussions are arranged alphabetically,
with related topics grouped arranged separately at the end.

BUBBLE UP FILTERS
     These are specific examples of internal filters.  These use
streams of air bubbles to push water up and out of a tube, thereby
creating a pull of water into the filter through the filter media. 
(See INTERNAL FILTERS).

CANNISTER FILTERS
     These are large plastic "cannisters" typically located outside
of and under the aquarium in the cabinet. They are designed with a
powerful pump which draws water through an in-take hose located in
the aquarium, pushes it at a relatively high pressure through the
filter medium, and forces it back to the aquarium through the
return hose.  (Many times, this water is sprayed across the surface
of the water to create aeration).

The question: "Which cannister filter should I buy?" is one of the most
frequently asked FAQs on *.aquaria and each time it comes up there
is discussion of the relative merits of each of the major brands.
 
General Comments:
 
Eheims:  The cadillac of cannister filters.  Very solid construction
    and operate virtually silently.  Significantly more expensive than
    other brands (see below).  Eheim recommends smaller models for
    larger tanks than the others and almost everyone buys larger than
    they say (2217 for a 55 gallon tank, for example, rather than the
    2213 which they recommend).  The Eheim cannister is a single
    hollow tube with water entering from a 90 degree tube at the
    bottom and flowing upwards through whatever you've packed in and
    pumped out the top.  They do not come with shut-off valves (a
    must-have for easy cannister maintenance), but these may be
    purchased separately (approximately $30).  Eheims have been dark
    translucent green with green hoses and black motor encasing.  The
    hose-clamping system is very solid.  Other options such as
    pre-filters, surface extractors and oxygen diffusers are available
    (and many will work with other brands).  They can also be ordered
    with built-in heaters (freshwater use only).  Made in Germany.
 
Fluvals:  Fluval filters have a slightly different design than the
    Eheims. Fluvals have the water enter and exit from the top of the
    filter. The entering water flows down around a central core which
    contains the filter media, and then returns up through that core
    to pass through the media.  The modular media containers which fit
    into the Fluval filter allow for easy changing/cleaning of any
    segment of the media without disturbing the others.  However there
    may be some small degree of media bypass from this design.  Flow
    rates are higher than the Eheim models.  Fluvals come with
    included on/off valves and a diffuser bar.  They recently were
    changed to a dark grey/black translucent color with beige hoses.
    Slightly older models are brown/tan with orange hoses.  There is
    no difference between the models except the color.  Fluvals are
    also very quiet, though not absolutely silent like the Eheims.  I
    sleep with one 2 feet from the head of my bed and can't hear it at
    night, however.  The hose-attachment clamps are screw-down type
    and can be hard to turn.  They are secure if attached correctly.
    Made in Italy.
 
Magnum:   Magnum recently changed their design from the 200/330 series
    up to the more modern 220/350.  The older models required oiling
    and generated a fair amount of noise compared with the others.
    The new models are magnetic impeller driven just like the Fluval
    and Eheims.  There is also a new Magnum product called the "HOT"
    magnum (Hang-On-Tank) which I have not evaluated. It appears to be
    an over-the-back filter which has a lower flow rate (250 gals) than
    the bigger Magnums, but require no hoses and may be easier to
    set up.  Magnums have traditionally been the cheapest option when
    buying a cannister filter.  Their design has the water entering
    the top of the filter, and being forced through a central
    container from the sides (as compared with bottom to top in the
    Fluvals) then to be pumped out the top again.  Magnum filters
    utilize a "cartridge" system which includes  carbon containers and
    micron cartridges.  The micron cartridges can be used with diatom
    powder to provide diatom filtration (see Diatom filters).  The
    filter cartridges are usually covered by a floss sleeve to provide
    coarse mechanical filtration.  Magnum filters provide a high flow
    rate but hold substantially less filtration media than the others.
    Construction is generally considered to be of cheaper materials
    than the other filters, with hoses being held on with rubber
    straps rather than screw down valves for example.  Magnums usually
    are a hot debating point in the cannister filter selection process:
    some people have had wonderful experiences with them and others
    have not been so lucky.  Made in America.
 
    Some functional information is below.  Numbers taken from
    manufacturers literature.  Keep in mind that flow rates will vary
    depending on what the unit is packed with and how high the water
    must be pumped.  The numbers listed below should be considered the
    maximum possible (they are generally listed with no media in
    place.  Additional backpressure will reduce flow substantially,
    especially on smaller models).
 
        GPH   Electric   Manufacturers  Cost (FAMA)
               Usage     Recommended    (US$ 1/94)    Filtering
              (watts)    Tank Size                    Volume
Eheim
------
2211:   80       5w      <40 gal.        $51            1 L
2213:   116      8w      <65 gal.        $56            3 L
2215:   165      15w     <90 gal.        $90            4 L
2217:   260      20w     <125 gal.       $130           6 L
2250:   380      ??      <265 gal.       $200           ??
2260:   500      ??      <400 gal.       $260           ??
 
Fluval
------
103:    103      7w      <25 gal.        $46            1.18 L
203:    111      7w      <50 gal.        $44            2.22 L
303:    222      15w     <70 gal.        $58            3.70 L
403:    317      22w     <100 gal.       $88           6.48 L
 
Magnum
------
HOT:    250      ??      ??              $58            ??
220     220      ??      ??              $45            ??
350     350      ??      ??              $55            ??

CHEMICAL FILTERS  (advanced)
     Ion exchange resins are used to deionize new water.  Also,
synthetic resins designed to adsorb specific ions (like phosphates,
or nitrates, or sulphates) are now available.  See ads in FAMA and
other such magazines for new items.  Thiel has chapters on chemical
filtration in his books, so does Moe (see Books).  Carbon is also a
form of chemical filtration.

DIATOM FILTERS  (advanced)
     These can be described as purely mechanical filters.  It relies on the
diatomaceous earth (skeletons of tiny animals called diatoms [Diatom comes
from the Greek: diatomos meaning "cut in two"]) which "cling" onto dirt and
a fine mesh screen to capture the "dirty" diatoms.  Because of the
efficiency, diatom filters are also called water polishers.  These are not
used over long periods (they clog up very quickly), and hence cannot be
considered good biological filters.

Diatom skeletons are composed of silica and there has been some
speculation as to whether usage in marine aquariums will lead to "brown
algae" explosions.
 
EXTERNAL FILTERS
     Oftentimes, this is used to denote power filters.  But this
not always the case.  (See POWER FILTERS)

FOAM FRACTIONATION
     See PROTEIN SKIMMERS.

INTERNAL FILTERS
     These filters are plastic cartridges that fit inside the
aquarium.  Dirty water is drawn into the filter through slits
located on either the top or sides of the body.  The method of
water propulsion can be motorized, or bubble driven.  Maintenance
of these filters can be difficult.  Many times, as one lifts the
filter out of the aquarium, dirty water backwashes out into the
tank.
     Some designs, like Lee's Triple Flow and similar models by
Penn Plax and Marineland do not have this problem.  They also cost
more, of course :-)  Also, one has to immerse entire appendages
into the tank to access the filter.  This type of filter is only
recommended for up to 20 gallons.  You may be surprised how
inexpensive external power filters (EPF) can be and how quiet they
are.  Always consider power filters unless you are raising fry,
spawning live-bearers or killies in a "natural" setup, or need
minimal flow (for spawning bubble-nest builders).

MECHANICAL vs. BIOLOGICAL
     Almost all filters perform mechanical filtration, and most
perform biological filtration.  The difference between these is
that mechanical filters will capture and remove suspended particles
from the water, clearing the water in the process. (The filter
media obviously becomes dirty, and must be cleaned every once in a
while).  Biological filters provide habitats for beneficial
bacteria that breakdown nitrogen compounds from biological waste
into progressively less toxic forms (ammonia -> ammonium ->
nitrites -> nitrates - > nitrogen).  (This is a gross over
simplification.  See nitrogen cycle in H20 quality).

POWER FILTERS
     This is the common name for filters that hang on the back of
the aquarium.  Two basic types exist.  In one case, water is drawn
through siphon action into the filter media, and expelled by a
pump.  In the second case, water is drawn by a pump into the filter
media and the allowed to trickle back into the tank.  A major
benefit of such a filter is the ease of maintenance.  The location
and design of the filter allows for quick and non-messy removal of
dirty filter media.

PRE-FILTERS  (advanced)
     This are filters used primarily to remove most of the
particles from the water before it arrives at a primary filter,
which may be located in a difficult to clean area.  The filter
media on pre-filters are removed and replaced easily, thus reducing
the number of times one has to change/maintain the media in the
primary filter.

PROTEIN SKIMMERS  (advanced)
     Protein skimmers, also known as foam fractioners, are an
unusual type of chemical filter.  They are primarily used in
marine aquaria, because they require the formation of foam which
form more readily in salt water.  Protein skimmers can be used in
freshwater, but will be less efficient, and may require greater
flows of air to produce sufficient foam.  They remove from the
water a wide variety of organic compounds (e.g.. proteins) that
normally collect on the surface of the tank water.
     These compounds, surface active molecules, are attracted to
the air-water boundary by their molecular structure.  Large amounts
of these compounds are often visible to the aquarist as slicks,
sheens, or thin scum on the tank surface.  In addition to the
presence of films on the surface of the water, an abundance of
these compounds is signalled by increased stability of bubbles
floating on the water.  This stability can result in large rafts of
bubbles spanning the surface of the tank, and very large bubbles
grown from many successive merges of smaller bubbles.
     A protein skimmer consists of a space where fine air bubbles
are encouraged to mix with circulating tank water, and a means for
collecting the resulting foam and removing this foam from the tank. 
Typically, a mist of fine bubbles is allowed to rise in a column of
circulating water, forming foam in a small chamber at the top of
the column.  This foam rises upwards through a narrow opening, and
flows into a collection cup which must be periodically emptied.  In
a properly adjusted protein skimmer, some amount of foam is present
all the time in the chamber, but will only rise high enough to
reach the cup and be collected when surface-active compounds are
present in sufficient quantity to stabilize the foam.

REEF FILTERS  (advanced)
     See WET/DRY FILTERS.

REVERSE UGF  (advanced)
     This uses the same gravel plate as a regular UGF except that
water is pumped down an uplift tube (in this case a misnomer),
under the plate, and then *UP* through the gravel.  The water
traveling through the uplift tube must be clean, since it would be
very difficult to clean under the gravel plate.  The water can come
from the output of a filter (cannister filter for example), or can
come from a new generation of powerheads (submersible centrifugal
water pumps) has a "reverse flow" feature which makes it easier to
use them for reverse flow UGF.  (See POWERHEADS).  The powerhead
should be outfitted with some sort of pre-filter such as a sponge.
     Since the mechanical filtration will have been taken care of already,
the reverse UGF is primarily a biological filter.  It has the alleged
benefit of keeping fish filth suspended in the water, or at least not being
sucked down under the UGF plate; allowing for easier removal during tank
maintenance/vacuuming.
     Because most aquarium equipment was not designed to work in
this manner, one typically has to rig up one's own hose adaptors to
connect the output hose to the uplift tube.
     Recently there have been several products designed specifically for
RUGF use.  Marineland is one company that sells RUGF units consisting of
powerheads, prefilters and connection tubing.  Other companies sell reverse
flow powerheads, but it is VERY important to use only systems which have
adequate pre-filtration, and not just pump water under the plates.

RO FILTERS  (advanced)
     These purely mechanical filters that are used to purify water
from the tap before introduction into the aquarium.  These devices
use a thin membrane that only allows water molecules (and a few
other smaller dissolved ions) to pass through to the output.  The
unwanted water and materials are redirected to the drain.  This
filtration method wastes water.  RO Filters can also be found at
building supply stores since household drinking water filtration
also uses the same technique.
     There are two common types of RO filters sold.  One uses a
cellulose tri-acetate (CTA) membrane, and the other uses a thin
film composite (TFC) membrane.  The TFC membrane is the best for
aquarium use.
     Because the rate of RO water production depends on water pressure,
temperature, and solute concentrations it is important to realize that
unless you have optimal levels of all those above you will probably
only get 50-80% of the production rate advertised.  Drops in
temperature below the 70 degree range usually measured (winter time,
for example) will drastically reduce production.

SKIMMER (see Protein Skimmer) (advanced)
     This term can refer to surface skimmers as well as protein
skimmers.  Surface skimmers are essentially boxes set just below
the surface level of the aquarium.  Water "spills" into this box
and is drawn out to a filter (by siphon or mechanical means).  This
oftentimes removes the surface "slick" found on marine aquarium.

SPONGE FILTERS
     These are open cell sponges that are connected to some
mechanical device (bubbler, power head, pump etc.) that will draw
water into the sponge.  Because of the large surface area/water
flow ratio, the suction is not strong enough at any given point on
the sponge to trap fry or other small fish (as opposed to, for
example, the intake hose of a cannister filter).  These are often
used for breeding tanks etc.  Fish filth is trapped in the sponge,
which is rinsed every once in a while for maintenance.  Most
sponges are shaped in such a way that, as filth clog up particular
areas, the suction collect waste in other areas.  The sponge also
serves as a biological filter.

TRICKLE FILTERS  (advanced)
     See WET/DRY FILTERS.


TURNOVER RATE
     The number of times the volume of water in the tank should
pass through the filtration system in an hour.  The general rule is
3-5 tanks/hour, unless the fish load is very light, in which case
.5-1 tanks/hour is OK.  Cannister filter instructions suggest 1-2
tanks/hour.  High turnover rates are probably beneficial (more
filtration), as long as the fish are not swimming for their lives
constantly.

UNDERGRAVEL FILTERS (UGF)
     This filter is a plastic plate with holes/slits that is placed
first in the aquarium, after which gravel is poured on top.  Water
is drawn through the gravel, and impelled up and out through uplift
tubes (typically located in the rear corners of the tank).  The
impelling method could be bubblers or power heads.  The gravel
becomes the filter media for both mechanical and biological
filtration.  This means that the gravel should be "vacuumed" every
once in a while.  As the gravel becomes clogged, water bypasses the
clogged areas, and these become sites for unhealthy bacterial
activity.
     There has been much debate over the use of UGFs.

WET/DRY FILTERS (advanced)
     These filters enhance the metabolic activity of the beneficial
bacteria by providing good conditions for their growth.  These are
very much in favor with marine aquarists, especially reef aquarists
whose guests require clean stable water.
     The principle of operation is as follows:  Water is sprayed
(by a revolving spray bar) or trickled/dripped (by a plate with
lots of holes) over a media that is largely exposed to air (i.e.
not immersed in water).  As the relatively random patterns of water
trickle over the media, the large surface of the media is
constantly kept wet with a thin film of water.  The large surface
area can dissolve lots of oxygen and may de-gas (expel) a number of
other things, most notably ammonia (NH3) and CO2.  The media houses
lots of bacteria which takes the oxygen and converts NH3/NH4+ into
NO2- (nitrite), and NO2- into NO3- (nitrate).  This is the "dry"
phase.
     The "wet" section is a submersed media which can be one or
both of the following: a purely biological filter, or a
denitrification filter.  A number of sources have been suggesting
that it contributes more to oxygen depletion than to any meaningful
nitrification.  A denitrification filter is created by placing a
large submerged sponge in the path of the water, allowing some
water to *slowly* flow through the sponge, while most of the water
passes over it.  In the nearly anaerobic cells of the sponge,
nitrites are converted to nitrogen by Pseudomonas and other
bacteria (however, Thiel and others have been very critical of this
method of denitrification); chemical "augmentation" -- a dolomite
or other calciferous material is used to leach calcium carbonate
into the water to replenish  what gets metabolized by plants; and
supplemental filtration, like a bag of activated carbon or some
Chemi-Pure. 

     The water which is relatively depleted of oxygen, is passed
into the wet phase, which supposedly converts the NO3- into
nitrogen and some oxygen.  This water then gets pumped back into
the tank.
     Wet/dry filters are not cheap, and because of this, the net
contributors often come up with suggestions for rolling your own. 
Keep your eyes peeled for these messages.

Filtration Related issues:
--------------------------

AIR FILTERS
     Some aquarists take the output of air pumps and bubble the air
through water in a closed jar.  The air is then taken through the
lid into the aquarium bubbler.  This serves to dissolve air borne
chemicals (such as mineral oils from the pump) in the jar water
before it gets into the aquarium.  Also useful for households that
have smokers.

GRANULATED ACTIVATED CHARCOAL/CARBON
     These are small pellets of carbon manufactured from organic
material (such as bones).  These pellets contain microscopic
caverns that are the right size to trap certain molecules or ions
(called adsorption as opposed to absorption).  After a period of 3-
6 months or so, the carbon becomes ineffective.  It cannot be "re-
activated" by heating in your home oven unless you have a blast
furnace at home.

OZONE
     Ozone is a highly reactive form of oxygen, and it is bubbled
through water in a special reactor to oxidize organic waste
material and some toxins (rendering them less harmful).  Since it
is so reactive, it is invariably bubbled through carbon (so
leftover ozone forms carbon dioxide) before being released into the
atmosphere.

PEAT
     This is an organic material made of composted forest fibers. 
Peat is rich in humic acid and tannin, and is sort of like tea. 
Its effect on water similar to tea.  It softens water and leaves
the water slightly acidic (and yellow).  It is used for lowering
and buffering water for sensitive fish.  Peat also helps chelate
some metals and make them usable by plants.  There are two
varieties of peat available: "normal" peat which consists of small
particles (much like peat used in gardening) and *fibrous* peat
that looks like a bunch of long strands and twigs (this is
sometimes referred to as "German" peat and it is nearly impossible
to buy in this country except in tiny, extremely overpriced
packages of Fluval and Eheim brand in aquarium shops.
     Garden peat can be bought dirt cheap in bulk from garden supply
stores.  MAKE SURE IT HAS NO FERTILIZERS OR FUNGICIDES -- these will kill
your fish.  According to Oleg Kiselev, Canadian peat, especially "Sunshine"
brand, seems to be safe.  Oleg has also used "Black Magic" gardening peat
with equal success.  ALWAYS RINSE PEAT BEFORE USING and many books
recommend you boil it a few times, too.  Oleg usually boils peat 3-4 times
and stores it wet.
     Peat is very important for killifish spawning.

POWER HEADS
     These are miniature pumps that draw water through uplift tubes
(associated with UGFs) and impel it into the aquarium.  They often
come with a feature that allows air to be drawn into the outflow
resulting in a fine mist of bubbles.  (This is due to something
called Venturi action).  The water output can usually be directed
in any direction, and up or down.  Some even have a reverse feature
for Reverse UGF systems.
     Although sometimes used as pumps, these are not really
designed to push water up any distance.  They are designed to draw
water and push it out laterally.

UV STERILIZERS
     Ultraviolet light sterilizers are used in series with  filters
to kill water borne parasites (such as ich) and/or bacteria. 
Although not strictly a filter, it does ultimately remove harmful
organisms.  When used in reef tanks or breeder tanks where the
occupants depend on microscopic organisms in the water for food,
these should not be turned on during feeding time.

ZEOLITE
     Zeolite is a naturally occurring mineral that can exchange
"hard" metallic ions (like magnesium and calcium) for soft metallic
ions (like sodium).  This softens water.  Zeolite also adsorbs
ammonia.  Zeolite will not work in salt water.  It is reactivated
by immersing it in a strong salt solution for 24 hours.

POWER FILTERS

A power filter is a box shaped filter that is hung on the back of an
aquarium.  An intake pipe projects down into the tank and the output of the
filter flows from spillway(s) on the body of the filter over the side of
the tank and into the tank.  The other major type of filter that is similar
to a power filter is the cannister filter.

Why use a power filter?  

1.  Space: These filters can be small relative to the volume that they pump
    through the filter.  They hang neatly over the side of the tank.  Most
    people put them on the back, where no one can see them, and where the
    space is wasted anyway.  *WARNING* All filters claim to pump a certain
    volume per unit of time.  This figure is sometimes tested by using
    clean (or no) filter media.  The actual volume pumped will start at the
    published value and decrease to zero if the filter media is not cleaned
    or changed.

2.  Noise: Power filters seem to be relatively quiet compared to other
    popular filters.

3.  Cost: The initial cost for a power filter is low.

4.  Easy of maintainance: Most of the filter media for a power filter is
    available prepackaged (but at additional cost).  Power filters provide
    easy access to the filter and media because it's part of the tank, in a
    convenient location.  Disassembly of the filter is straightforward and
    simple. Some filters will also allow you to insert media that was not
    specifically designed for that filter.  Some filters are designed for
    you to throw away your biologically active media if you follow the
    manufacturer's instructions (this is bad, see below).

Major Manufacturers of Power Filters 
	(GPH = US gallons/per hour).
	Prices are approximate mail order prices in $US.

		Name 	GPH	$	GPH/$
Aquaclear	Mini	100	10	10
(Hagen)		150	150	14	10.7
		200	200	14	14.3
		300	300	21	14.3
		500	428	38	11.3

Whisper		Compact	100	10	10
(Second Nature)	1	150	13	11.5
		2	200	14	14.3
		3	300	21	14.3
		5	400	31	12.9

Penguin		110	110	12	9.2
w/biowheel	160	160	14	11.4
(Marineland)	300	300	22	13.6

Canistar	MX	155	18	8.6
(Penn-Plax)

Supreme Aquamaster PME 	120     14	8.6  	
        Aquamaster PMSW  ?      25  	
        Aquamaster PLSW 300     29  	10.3	
        Aquaking        300     32  	9.4
        Superking       600     41	14.6

Overview of Perceived Performance.

Mechanical Filtration/Chemical Filtration

The key to mechanical and chemical filtration with a power filter is the
amount of media that the water must pass through.  Ideally, all the water
that passes through the filter also must pass through all of the media.

The Aquaclear and Canistar filters should work the best at
mechanical/chemical filtration.  They push all the input water through all of
the media.  The Aquaclear will allow water around the media if the media is
clogged.  Look for backflow coming out near the siphon tube.  The Whispers
and Penguins (except the Penguin 300) design allow some of the water to
pass by the chemical filtration (carbon, ammo-chips etc.), but all the
water must pass through the dacron mesh.  The Penguin 300 has a "media
basket", 2 removable containers in the filter body so you can add your own
media to help filter the water, this design addition makes it difficult for
any water to pass by the media.  The diatom water polishing mode on the
Canistar seems to be iffy.


Biological Filtration

The main concern here is whether or not you throw away the bacteria's happy
home when it comes time to clean the filter.  There is probably little
difference in the performance of dacron vs. foam for harboring bacteria.
	
The Aquaclear has a foam insert to harbor helpful bacteria.  You may rinse
it and put it back in the filter, without ever buying new foam.  No helpful
bacteria are lost if this is done correctly.  Also the "force all the water
through the filter" concept discussed above applies here too, all the water
must pass over the bacteria, which may clean it better.  A caveat is that
the fast flow through the sponge does lower the ability of the filter to
get rid of NH4 in 1 pass, but the increased volume over a typical cannister
filter may make up for that.  The Whisper's, Penguin's and Canistar's'
dacron pad eventually must be thrown out, thus losing the bacteria.
Ingenious solutions have been invented to minimize this problem, but IMHO
the Aquaclear is superior in this regard.  The Penguin is like the Whisper,
except that it has an added device called a Bio-wheel.  It probably helps,
but there are mixed reports on this.  The wheel may need regular,
infrequent maintenance to prevent clogging.

The Supreme models are unique in that they do not use the troublesome
magnetic-impeller water-immersed motors.  Their motors are large industrial
air-cooled ones that sit on top of the filter and run the impeller via a 
plastic shaft.  Also, they use siphon tubes to bring the water into the filter
box, and pump the filtered water back to the aquarium, preventing the impeller
from shredding and thus reducing the particle size in the influent.

Other gotchas/Special features

The Aquaclear has good sponge media, and allows the use of media bags so
you can fill your own.  The carbon bags cost a bit, but they seem to use
good carbon.

The Penguin biowheel has a tendency to stop if it gets dirty.  If the wheel
isn't' turning, it isn't working.

Power consumption

   Not all equipment really consumes the amount of power that it's
rated for.  If you want an accurate measurement of your power
consumption, it may be possible to borrow a Kilowatt-hour meter from
your local utility company.  Not everyone answering the phone will
know what you want, but be determined.

The meter is placed in line with your equipment, so you will need to
rewire your tank so that all of the items to be monitored are plugged
into the meter.  The meter is similar to the one that comes into your
house, except that it is configured for 120V 2 wire.  The meter has a
granularity of one kilowatt hour, so if you're measuring something
that draws little power, it may take a while to get an accurate
reading.

Summary

There are no clearly superior filters here, although the Whisper seems to
lose in almost every category (your mileage may vary).  The Aquaclear
series is probably the best overall, however, if you need a big filter, the
Penguin 300 may be better because it has the Bio-Wheel and the media
baskets.

AIR PUMPS:
----------

Keep away from cheap pumps.  Make sure they are UL listed (as you should
with all other electrical devices you are planning to use with your
aquarium).  Listen to the pump (under load!) before you buy it.  If you can
hear it in the noisy petshop, imagine what it will sound like in your
silent house at 2 AM.  It is also a good idea to get a pump that is not too
much more powerful than you need - more powerful pumps are invariably more
noisy.

As a general rule, "adjustable" air pumps are worth extra money
only if the adjustment is electronic, rather than by a by-pass
valve.  The former is more quiet.  Make sure your pump is
positioned above the water level of your tank, because power
failures and other events can cause water to back-siphon into the
pump and flood it.  You can also use "check-valves" available at
pet shops to make certain that this does not happen.

The following is from Spass Stoiantschewsky:

spass@midas.wr.tek.com

and the last name is spelled "stoiantschewsky", my system
has it spelled wrong...always has, probably always will...

the address will probably change, but i haven't the faintest
idea when...it should have already changed...

best pump tested at depth to date: Tetra luft g 
best pump volume (shallow depth) to date: whisper 1000
noisiest pumps: whisper
quietest pumps: challenger (?), followed closely by Tetra and
silencer.

best buy in pumps: Tetra luft g

noise level measurements are purely by ear.

i'd like to talk to people who have pumps they particularly like 
or dislike and anyone who has pumps that haven't been tested (easy
test).
untested pumps: schego, iwaki, wisa, supra 
tested pumps: whisper, silencer, Tetra, challenger

[Ed. Note.  Spass will post a more complete article soon. ;-) ]

CHILLER SIZING
--------------

Water Temperature Pull Down From Room Temperature (Degrees Fahrenheit) *
               5o      10o      15o      20o      25o
             ----     ----     ----     ----     ----
Horsepower  
----------
1/6           200      100       67       50       40
1/5           560      280      187      140      112
1/4           800      400      267      200      160
1/3          1000      500      333      250      200
1/2          1440      720      480      360      288
3/4          2600     1300      867      650      520

		              Tank Size     
			      ---------
* Tank sizes represent the maximum volume for each horsepower and
temperature combination.  To provide a margin of safety, add
20 percent to the tank volume when determining chiller requirement.

Reprinted with permission from _Aquarium Fish Magazine_, Vol. 5,
No. 3, December 1992.


Disclaimer:
-----------
Some answers listed above may reflect personal biases of the author
and the FAQ's contributors.  In cases where the answers name
specific products and their respective manufacturers, these are not
to be taken as endorsements, nor commercials for the manufacturer. 
Where cost information is stated (magazine subscription rates),
this is based on "street" information, and are in no way binding on
the publisher.  The answers contained in this series pertain to
discussions on the rec. and alt.aquaria newsgroups, and are by no means
exhaustive.  This series is not intended to take the place of good
aquarium books on the subject matter.

Copyright:
----------
The FAQ owes its existence to the contributors of the net, and as
such it belongs to the readers of rec.aquaria and alt.aquaria. 
Copies can be made freely, as long as it is distributed at no
charge, and the disclaimers and the copyright notice are included.