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The Building of a
Reef (Tank)
Tank maturity seems to be even more of an issue
without the sand bed. The sand bed just takes some time to get
enough nutrients in it to sustain populations and stratify into
somewhat stable communities and become functional. So, here's the
tank reason, and then I'll blow into some ecology for you. When you
get a tank, you start with no populations of anything. You get live
rock to form the basis of the biodiversity - and remember that
virtually everything is moderated by bacteria and photosynthesis in
our tanks. So liverock is the substrate for all these processes, and
also has a lot of life on it. How much depends on a lot of things.
Mostly, marine animals and plants don’t like to be out of water for
a day at a time...much less the many days to sometimes a week that
often happens. So, assuming you are not using existing rock from a
tank, or the well-treated aquacultured stuff, you have live rock
that is either relatively free of anything alive to begin with, or
you have live rock with a few stragglers and a whole lot of stuff
dying or about to die because it won’t survive in the tank. Some, if
not most, rock exporters have a “curing process” that gets rid of a
lot of the life to begin with and some of this is to keep it from
dying and fouling further, but some of it would have lived if
treated more carefully.
From the moment you start, you are in the negative. Corallines will
be dying, sponges, dead worms and crustaceans and echinoids and
bivalves, many of which are in the rock and you won't ever see. Not
to mention the algae, cyanobacteria, and bacteria, most of which is
dehydrated, dead or dying, and will decompose. This is where the
existing bacteria get kick started. Bacteria grow really fast, and
so they are able to grow to levels that are capable of uptaking
nitrogen within...well, the cycling time of a few weeks to a month
or so. The “starter bacteria” products give me a chuckle. Anyone
with a passing knowledge of microbiology would realize that for a
product to contain live bacteria in a medium that sustains it would
quickly turn into a nearly solid mass of bacteria, and if the medium
is such that it keeps them inactive, then the amount of bacteria in
a bottle is like adding a grain of salt to the ocean compared to
what is going to happen quickly in a tank with live rock in it.
However, if you realize the doubling time of these bugs, you would
know that in a month, you should have a tank packed full of bacteria
and no room for water. That means something is killing or eating
bacteria. Also realize that if you have a tank with constant
decomposition happening at a rate high enough to spike ammonia off
the scale, you have a lot of bacteria food...way more than you will
when things stop dying off and decomposing. So, bacterial growth may
have caught up with the level of nitrogen being produced, but things
are still dying...you just test zero for ammonia because there are
enough bacteria present to keep up with the nitrogen being released
by the dying stuff. It does not necessarily mean things are finished
decomposing or that ammonia is not being produced.
Now, if things are decomposing, they are releasing more than
ammonia. Guess what dead sponges release? All their toxic
metabolites. Guess what else? All their natural antibiotic compounds
which prevents some microbes from doing very well. Same with the
algae, the inverts, the cyano, the dinoflagellates, etc. They all
produce things that can be toxic – and sometimes toxic to things we
want, and sometimes to things we don’t want. So, let's just figure
this death and decomposition is going take a while.
OK, so now we have a tank packed with some kinds of bacteria,
probably not much of others. Eventually the death stops. Now, what
happens to all that biomass of bacteria without a food source? They
die. Some continue on at an equilibrium level with the amount of
nutrients available. And, denitrification is a slow process. Guess
what else? Bacteria also have antibiotics, toxins, etc. all released
when they die. But, the die-off is slow, relative to the loss of
nutrients, and there is already a huge population, and yet you never
test ammonia. "The water tests fine.” But, all these swings are
happening. Swings of death, followed by growth until limited, then
death again, then nutrients available for growth, and then
limitation and death. But, every time, they get less and less, but
they keep happening – even in mature tanks. Eventually, they slow
and stabilize.
What's left? A tank with limited denitrification (because its slow
and aerobic things happen fast) and a whole lot of other stuff in
the water. Who comes to the rescue and thrives during these cycles?
The next fastest growing groups...cyanobacteria, single celled
algae, protists, ciliates, etc. Then they do their little cycle
thing. And then the turf algae take advantage of the nutrients (the
hair algae stage). Turfs get mowed down by all the little amphipods
that are suddenly springing up because they have a food source.
Maybe you've bought some snails by now, too, or a fish. And the fish
dies, of course, because it may not have ammonia to contend with,
but is has water filled with things we can't and don't test
for...plus, beginning aquarists usually skimp on lights and pumps
initially, and haven't figured out that alkalinity test, so pH and
O2 are probably swinging wildly at this point.
So, the algae successions kick in, and eventually you have a good
algal biomass that handles nitrogen, produces oxygen through
photosynthesis, takes up the metabolic CO2 of all the other
heterotrophs you can’t see, the bacteria have long settled in and
also deal with nutrients, and the aquarium keeper has probably
stopped adding fish for a spell because they keep dying. Maybe they
started to visit boards and read books and get the knack of the tank
a bit. They have probably also added a bunch of fix-it-quick
chemicals that didn’t help any, either. Also, they are probably
scared to add corals that would actually help with the
photosynthesis and nutrient uptake, or they have packed in corals
that aren't tolerant of those conditions.
About a year into it, the sand bed is productive and has stratified,
water quality is stable, and the aquarist has bought a few more
powerheads, understands water quality a bit, corallines and algae,
if not corals and other things are photosynthesizing well, and the
tank is "mature." That's when fish stop dying when you buy them (at
least the cyanide free ones) and corals start to live and grow and I
stop getting posts about "I just bought a coral and its dying and my
tank is two months old" and they start actually answering some
questions here and there instead of just asking questions (though we
should all always be asking questions, if not only to ourselves!).
So, ecologically, this is successional population dynamics. Its
normal, and it happens when there is a hurricane or a fire, or
whatever. In nature though, you have pioneer species that are
eventually replaced by climax communities. We usually try and stock
immediately with climax species. And find it doesn't always work.
Now, the "too mature" system is the old tank syndrome. Happens in
nature, too. That whole forest fire reinvigorating the system is
true. Equally true on coral reefs where the intermediate disturbance
hypothesis is the running thought on why coral reefs maintain very
high diversity...they are stable, but not too stable, and require
storms, but not catastrophic ones....predation, but not a giant
blanket of crown of thorns, mass bleaching, or loss of key
herbivores.
This goes to show what good approximations these tanks are of
mini-ecosystems. Things happen much faster in tanks, but what do you
expect given the bioload per unit area. So, our climax community
happens in a couple years rather than a couple of centuries. Thing
is, I am fully convinced that intermediate tank disturbance would
prevent old tank syndrome.
My advice on starting tanks is to plan the habitat you want. Find
the animals and corals you like. Learn about the tiny area of the
reef you will try and recreate, and do not try to make a whole coral
reef in one tank. Then, purchase the equipment required to emulate
that environment. Then, add the appropriate types of substrate
(sand, rubble, rock, whatever) and wait long after “your tank water
tests fine” before you add fish and corals. First, add herbivores
and maintain water quality. Water changes, carbon, skimming,
alkalinity, calcium. Keep the water of high quality, even for things
you can’t test for. Wait a few months and enjoy the growth that will
happen. Then, add some of the species that you plan to
keep….invertebrates and corals. They help create the environment,
and also photosynthesize, add biodiversity, stabilize nutrients,
etc. Then….then….add fish. The fish will have a reef as their new
home. They won’t be stressed by this variable bouilllabaise of water
and a strange habitat that keeps changing as things are added or
die. They will have a stable tank with real habitat, and then the
original concept you imagined will have happened.
Eric Borneman
The original article can be found here - "The
Building of a Reef (Tank)"
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