This reminds me of how confusing things were when I first got started.
I read a couple of good books ( a couple of times each ) before I
started to "get it". I'll try to summarize a little here.

Biological wastes are broken down by bacteria. Much of the waste
products we're concerned with here are nitrogen based.

These wastes are first tackled by bacteria type 'A' and converted to
Ammonia. Ammonia is very toxic.

Ammonia is then used by bacteria type 'B' and converted to Nitrite.
Nitrite can be very toxic under some conditions.

The Nitrite is then converted to Nitrate by bacteria type 'C'.
Nitrate is only toxic at very high levels but it is a nutrient source
for plants and algae.

Nitrate is then broken down into Nitrogen gas by bacteria type 'D'.
Nitrogen gas is safe and will escape from the aquarium via little
bubbles.

So, the first thing you'll need to do is establish a population of
bacteria type 'A' and then bacteria types 'B' and 'C'. This is what
people mean when they talk about cycling a tank. They are providing
enough food for the bacteria to colonize and start the process of
converting Ammonia - Nitrite - Nitrate. Luckly these bacteria are
everywhere, in the air, on our bodies, in dirt etc... These colonies
of bacteria will start to flurish in a couple of weeks provided they
have a food source and a substrate to grow on. That's where the
filters come in. Filters typically try to provide a huge amount of
surface area for the bacteria to grow on. Some also provide some
mechanical filtration to trap particles.

So far we have a filltration system that converts biological wastes
into Nitrate, but Nitrates will cause serious problems do to
excessive algae, so we try to keep the Nitrate levels low.
The problem is that the bacteria that converts Nitrate to Nitrogen gas
requires conditions very different from the the other bacteria types (
'A', 'B', and 'C'). The first 3 types of bacteria require alot of
oxygen to do their job while type 'D' requires a low oxygen
environment.

Most biological filters do an awesome job at growing the first 3 types
of bacteria but not the last one so that Nitrates build up in a system
quickly. The first step is to try to remove waste from the system
before the bacteria gets to it. This is where the protein skimmer
comes in. Secondly, the mechanical filters have to be cleaned at
least once per day, otherwise they are just trapping wastes in the
system which will eventually turn into more Nitrate.

What we really want is a system that provides alot of high oxygen
surface area for bacteria types 'A', 'B', and 'C' and also low oxygen
areas for bacteria type 'D'. Liverock and a deep layer of sand (deep
sand bed , DSB) provide these environments in a very natural way.
Even if you provided an environment for bacteria type 'D' via a second
filter system, or via a DSB, the Nitrates are still in the water
column long enough for algae to get out of hand.


Clear as mud?
Here are a couple of articles by people far more knowlegable than I.
Not to mention they write gooder two.

Good luck.

The Basics of Filtration for the Reef Aquarium
http://www.advancedaquarist.com/issu...3/beginner.htm

These people are a little weird but they have a lot of good info
online. Look at the stuff about the "bullet proof reef"
http://www.garf.org



On 30 Aug 2004 13:40:45 -0700, (Dale & H) wrote:

... trade the cannister filter in for it.

... cannister filters are not really a good choice for a reef
tank,

Thanks for the feedback guys, but I am not sure I understand. From the
reading we have done and from conversations with dealers, we were led
to believe that a biological filter was required to convert Amonia to
Nitrite then Nitrite to Nitrate, with the latter being much less
harmful and cleared out through water changes. The dealer who sold us
the tank also sold us the 204 on the basis that we needed more
biological filtration capacity than the Juwel 240 integral filter
provided (which is apparently rated for fresh water tropicals only).
The feedback here seems to suggest that the skimmer can be used in
place of the biological filter(?). Or is it that the 204 type
cannister filters are bad news but other biological filters are OK(?).
One dealer we consulted suggested under-gravel filtering, but others
seem to agree with the first and recommend cannisters?

Since our original posting, we visited a dealer we haven't been to
before and he too recommended a skimmer, but in addition to the
existing filter setup.

Help!!