The “Old Tank” Syndrome

The success that reef keepers have achieved in the last ten
to fifteen years has been nothing short of spectacular. It is
now possible to keep many of the fish and corals that only a
short time ago were thought to be impossible to keep. This
process has required us to learn many things that previously we
had not even thought about. In the early days of the saltwater
hobby before the nitrogen and other cycles were fully
understood, many hobbyists had to suffer from what was called
“new tank syndrome.” This usually occurred soon after a tank
was set up and a few fish were added and then for some unknown
reason they all would perish. Fortunately once the nitrogen
cycle was understood and the need for developing a bacterial
filter common practice, this syndrome was no longer a problem.
Now that a tank no longer needs to be broken down and tanks are
being maintained for long periods of time a new “syndrome” is
starting to show itself. For lack of a better term the
situation is being called the “Old Tank Syndrome.” This
syndrome is not as dramatic as the new tank syndrome where all
of the fish died, but it can be just as unsettling to the
tank’s owner.


Over time, big stag horn Acroporas and
other large corals will eventually slow the flow of water
throughout the tank

The best way to describe this syndrome is simply that the
tank is failing to thrive. For those of that have had reef
tanks for an extended period of time we know when looking at a
tank whether it is thriving or whether it is simply holding its
own or failing. In the case of a tank that is going through old
tank syndrome it is starting to decline. This situation usually
occurs after a tank has been set up for five years or longer,
although it can occur earlier. The syndrome is usually the
result of a number of factors working together to cause the
demise of the tank, although a single factor if it is great
enough can also lead to the problem. In this article I will
address each of the possibilities for its cause individually as
well as their possible solutions, in the hope of helping those
who have a tank suffering from it to bring it around.


Benign Neglect

The single biggest cause for a tank to suffer this syndrome
is actually the result of its success. As a tank ages and the
corals and fish thrive and grow a number of things start to
happen. Fewer new additions are made to the tank due to space
limitations and as a result the excitement that occurs when a
new fish or coral is added no longer occurs. (As a side note we
need to admit that this hobby is very addicting and adding
something new is kind of like a fix for us that gets us all
excited again and keeps us motivated to keep the tank at an
optimum level). In addition, this success leads to the feeling
that what we are doing is working, so we do not need to change
or improve upon our techniques even as the tank is changing
itself. A saltwater aquarium is not a static entity, it is a
fluid one, no pun intended, and therefore we need to constantly
tinker with the system to keep it at an optimum level.


Algae will even grow in the outflows when the
nutrient levels are high as it is difficult for herbivores to
reach these areas.


A large fish population can lead to a more rapid
demise of an older tank.

This not changing what we are doing is not the major cause
of why a tank is no longer thriving, it is more of a result of
our getting a little lazy and taking for granted that we have
become experts at managing the tank. As a result, we tend not
to do the tedious things necessary to keep a tank at its
optimal level or if we do them we do not do them with the same
frequency that we did when the tank was thriving. After
observing several hundred successful tanks it has become
apparent that the tanks that continued to thrive over the long
term were the ones where the owner continued to take meticulous
care of them. They did not cut corners or reduce their level or
frequency of care despite the tank doing well. That is why I
placed this section first, in that even if some of the later
topics occur, as long as neglect of the tank does not take
place the tank will still probably do well.


Nutrient Levels

A saltwater aquarium is not just a tiny piece of the ocean,
despite some authors trying to convince us that it is. If we
are lucky it will contain some of the same attributes as the
ocean but it will always be just a very tiny closed replica of
the real thing. One of the major attributes that it will be
lacking is size. With this it will also lack the dilution
factor that is critical for keeping harmful compounds from
accumulating to toxic levels. In the ocean a small amount of
nitrate, phosphate or even a heavy metal will not be
deleterious to the entire system. In a closed saltwater system
however, high levels of any nutrient good or bad will have a
negative impact on the system. In a closed saltwater system,
one of the factors that lead to old tank syndrome is that over
time nutrients will tend to accumulate.

The two major nutrients that will accumulate over time are
nitrogen and phosphorous. With large frequent water changes or
with the use of resins or specially designed filters it is
possible to keep the levels of these compounds low. However as
a tank ages and as fish and corals grow these compounds
containing these nutrients tend to increase faster and faster.
Unless this increase in production of these nutrients is noted
and steps are taken to control this increase, these nutrients
will become problematic. The first sign that nitrogen or
phosphorus containing compounds are becoming a problem is when
algae begins to grow in the tank. Algae can grow amazingly fast
and while a few tufts of algae on the rock or substrate are not
a reason for concern, they should raise a red flag that the
nutrient levels are on the rise. However, it should also be
realized that nitrate and phosphate levels can be high and
algae still might not be present if a large number of
herbivores are present. These nutrients have other deleterious
effects besides causing algae overgrowth including inhibiting
calcification among corals and causing tissue recession from a
coral skeleton to name just two of the problems associated with
high levels of them.

As noted above doing things less frequently is often one of
the things that lead to a tank’s not thriving. In this instance
the thing that is not done is regular water testing. Regular
water testing is essential to maintaining high water quality.
When nitrate or phosphate levels begin to rise several things
can be done. First more frequent and larger changes with pure
aged water should be done. Larger than normal water changes in
the 25-50% range are necessary as otherwise the dilution and
removal of these nutrients is so small that little is removed
and the problem lingers or becomes worse.


Detritus can accumulate in the substrate over time
if inadequate micro fauna are not present and lead to problems
in the tank.

If large water changes do not result in the desired
diminution of these nutrients then other steps need to be
taken. Iron-based phosphate removing resins have increased in
popularity within the hobby over the last few years for good
reason. These compounds are very good at pulling phosphate as
well as heavy metals from the water in a relatively short time.
They have proven to be relatively harmless to the tank’s
inhabitants including delicate fish and corals. The only
shortcomings they seem to possess are the potential to bind
with carbonate upon their introduction and consequently pull
down the carbonate hardness of a tank for a short period of
time and their high cost. Therefore they should be gradually
introduced and the carbonate hardness should be tested
frequently during their introduction. Nitrate levels can be
reduced through several means including the use of refugia
containing macroalgae as well as nitrate filters containing
anaerobic or anorexic bacteria. For large tanks, a large
refugia may be required that may be prohibitive because of its
size. Low oxygen filters on the other hand can be relatively
small and still remove a great deal of nitrate, but they
require significantly more attention and can cause major
problems if not maintained properly.

In addition to these nutrients, dissolved organics can also
be problematic in an older tank. Signs that this is occurring
is that red or black slime, cyanobacteria, begin to form on
some of the live rock or on the substrate. Once again as a tank
ages and the corals and fish grow the bio-load of the tank
increases, that will cause a larger production of these
compounds to occur. In addition, filtration equipment such as
protein skimmers will tend to function at a lower level over
time. In most tanks, water motion will also slow or be reduced
over time due to equipment aging and corals growing and this
will allow detritus to accumulate. As a result, these factors
will work together to cause the organic load within the tank to
increase. Even if slime algae does not occur, higher organic
levels can be seen simply by the water having a yellow tint to
it. Keeping dissolved organic levels low usually requires
several things in addition to the increased larger water
changes discussed above. Detritus should be removed at every
opportunity during these water changes and at no time should
large piles of detritus be allowed to accumulate in any one
spot. This may require the addition of more water flow within
the tank and this flow should be focused along the bottom of
the tank to keep detritus in the water column as long as
possible so that the filters can remove it. Also when the water
is becoming yellow or when slime algae occurs, carbon should be
added to the filtration regimen as it is very efficient at
removing both yellowing compounds and dissolved organics, but
it does become exhausted quickly when these compounds are
present in large amounts. Lastly, the protein skimmer should be
broken down and cleaned to make sure that it is producing at an
optimal level.


Trace Elements

Just as a home aquarium does not contain enough volume to
adequately dilute away harmful nutrients, it also does not
contain enough volume to supply essential trace elements. As a
result over time, some critical trace elements are depleted to
such a level that they are no longer present for corals and
other animals to consume. At this point, they become the
limiting factor for the growth and health of some animals.
Unfortunately it is difficult to measure the levels of most
trace elements. Fortunately though, many of these trace
elements are replenished through regular water changes, so no
additions are necessary. However, in some older tanks it may
still be a good idea to add a small amount of a wide variety of
trace elements on a regular basis. Always start with less than
the recommended amount to make sure that the additive is doing
no harm. Then gradually build up to the desired amount, which
should not exceed the manufacturer’s recommended dosage.

Foods and Feeding

In addition to inadequate trace elements causing problems in a
tank over time, improper or inadequate feeding of both the fish
and corals can also cause a tank to look old before its time.
Just as you would not want to eat steak or lobster alone for
every meal despite how good they taste, the same is true or our
tank’s inhabitants. We not only need to supply foods in
adequate quantity and quality, but we also need to supply
adequate variety. On the reef, where we get most of the fish
for our tanks, most fish consume 60-70% of their diet in plant
material. Unfortunately most of the foods we feed our fish are
80% protein. While this may be fine for lionfish and moray
eels, for most other fish this leads to malnutrition or a
vitamin deficiency over time. As a result fish that we keep
long term in our tanks start to look long in the tooth or worse
in a relatively short time. Most of the fish we now keep have
been kept successfully in closed systems for over 20 years. If
we want to keep our fish looking vibrant and healthy for this
long we need to improve our feeding techniques for them as well
as provide foods that provide adequate nutrition.


Herbivores like the sea urchin can help keep algae
in check, but may mask that nutrient levels are high.

Anyone that has seen a fish that has been kept in a tank
with less than optimal food will notice right away that it no
longer looks as vibrant as when it was added to the tank. For this
reason it is apparent that we need to supply our fish with
significantly more foods that contain the compounds that not
only keep them healthy, but also keep them vibrantly colored.
There are now foods available, fresh, frozen, and freeze dried
that contain not only high levels of plant material, but also
that contain essential pigments to keep the fish looking
vibrant. If none are readily available you can even prepare
your own food mix using foodstuffs available at the fish market
and grocer using recipes found easily on the Internet. It is
not only crucial to feed these foods, but it is just as
important to feed them properly. Feeding should be done
frequently in very small amounts. The stomach and digestive
tract of most fish are very small. They are designed for the
constant consumption of small amounts of food rather than to
take in a large bolus of food in one big meal. Unfortunately,
feeding one large meal to our fish per day is how it is usually
done. This methodology too needs to change in order to prolong
the health and vibrancy of our fish long term.

In terms of feeding coral and other invertebrates, only now
are we starting to understand the need to feed these animals.
Most of us assumed that adequate light and the extra food and
waste from our fish would be more than adequate to supply the
nutritional needs of our corals. However, when analyzing the
structure of a coral polyp it becomes apparent how crucial food
intake is when one realizes that 60% of a coral polyp’s body is
designed for food intake. It is highly unlikely that this much
of the coral’s body would be dedicated to such an endeavor if
it were not critical for the long-term health of the animal. In
terms of animals looking less than optimal as is the case in
old tank syndrome, inadequate nutrition for the invertebrates
may at least partially explain this along with the other
factors previously discussed. When the corals are small it may
be possible for them to obtain all of the nutrition they need
from the light and from the extra food and fish waste floating
around. However as the colonies get larger and competition
between corals for food and space more intense it is likely
that the nutritional needs of the invertebrates are no longer
being met and hence they no longer look to be in optimal



Detritus settles everywhere including the sump,
which needs to be cleaned out regularly.


Excessive algae growth is indicative of
excessive nutrients being present.

I have been conducting a relatively simple experiment for
the past year in my own relatively older systems (both over 5
years of age). In one tank the invertebrates are on their own and only get
nutrition from what is left over from the fish or what they take from the
water. In the other system the corals are fed directly three times a week
with different foods. For the first six months there was virtually
no difference in the overall health of the corals or the tank
in general. However over the last six months I have noticed a
significant difference. The corals in the tank being fed have
grown significantly more than those in the tank that was not
fed. (I know this is probably not a big surprise). But the big
surprise is that the corals in this tank also suffered
virtually no losses while several colonies in the non-fed tank
perished or suffered tissue loss at some point. After observing
this first hand it is now my opinion that feeding the corals
and other invertebrates on a regular basis will go a long way
in keeping them from pushing the tank into looking


One of the other causes of tanks looking old is that over
time many pests become problematic. Flatworms, aiptasia, red
bugs, Majano anemones parasitic brittle stars and other pests
tend to reproduce and thrive in closed systems where predators
are not present. When a tank is first set up and often over the
first few years these pests are usually not in adequate numbers
to be a problem. Over time and with a ready food source these
animals can constantly irritate or even kill many sessile
invertebrates. For this reason it is essential that pests be
removed or killed as soon as they are spotted in a new or
relatively new tank, lest they reproduce to harmful levels.
There are now numerous accounts of how thriving tanks needed to
be completely broken down as a result of these pests
overrunning the tank. While these are extreme cases, even small
numbers of these pests can make the animals in an old tank look
damaged or sickly.

Speciation / Competition

The opposite of having the corals in an old tank look less
than optimum due to parasites is to have them look this way due
to speciation. Speciation is the process whereby one animal or
plant species dominates a locale after multiple species were
present. The best example of this is an old growth pine forest.
In this type of forest only pine trees thrive. This is due to
the pine trees themselves producing compounds in their needles
that prevent other plants from growing. As a result as the pine
tree drops its needles the compounds in the needles act as an
herbicide and prevent other plants from growing under or with
the pine trees.

In a saltwater tank, especially one housing soft corals such
as Sarcophytons, Xenia, Sinularia or
Cladiella one of these species will tend to dominate
over time. All of these corals produce terpenoids or
sarcophytenes. These chemicals just like those found in pine
needles act to inhibit the growth of competing animals. As a
result, as a tank ages the animals that produce the most growth
inhibiting of these compounds will tend to dominate. This same
type of phenomenon also happens on the reef where huge stands
of a single species of soft coral occupy specific areas of the
reef. While having only one type of coral in a tank actually is
probably more representative of a section of the reef, most
hobbyists do not like this look and desire diversity. However,
the corals present will still produce terpenoids to try and
produce this result. This production of growth inhibiting
compounds does take its toll over time and the result once
again is corals and other invertebrates that look less than

There are several things that can be done to prevent this
from occurring. First, water changes, once again, and the use
of carbon can help to dilute the concentration of these growth
inhibiting compounds. In addition, it may be necessary to thin
out or reduce the size of large soft coral colonies. This is
necessary in that larger colonies can produce larger amounts of
these compounds. So in order to prevent one species from
dominating a tank, it may be necessary to “prune” the corals to
keep them all to relatively equal size or of an equal ability
to produce toxic compounds.

Competition between corals is another factor that may cause
corals to look sickly. If two or more coral colonies have to
constantly battle each other for space, nutrition, etc., these
battles consume a lot of the animal’s energy. As a result the
corals lose a lot of their vitality. For this reason it is
essential to give the corals lots of space when initially
setting up a tank to try and reduce this competition. When this
is done an interesting phenomenon occurs, especially with stony
corals. The corals will eventually grow to the point where
their bases almost touch each other. But at this point they
kind of form a demilitarized zone where neither coral grows
into the other. This behavior allows both corals to thrive
without requiring either coral to devote a lot of energy to
defending itself or attacking its neighbor unlike what occurs
when two corals are placed too close together.

Diminished Diversity in live rock and sand

One of the great attributes of new live rock is the vast
diversity of life that it contains. Mysis, shrimp, copepods,
worms, crabs and numerous sessile invertebrates abound on this
substrate. A new substrate is also often colonized from the
animals in the rock so it to can hold a large number of
different organisms. Over time however, the diversity in the
rock tends to be reduced. Microfauna are consumed, reproduction
in some species does not occur in closed systems, the substrate
becomes clogged with detritus and the overall variety of life
diminishes. This diversity does not simply exist in the rock
and substrate, it helps remove waste, it is consumed by the
fish and corals it keeps the substrate oxygenated, etc. As a
result, it is possible that as the diversity of this life is
reduced, the overall health of the tank may be reduced as well.
To try and keep this from happening new live rock that has been
properly and completely cured should be introduced from time to
time. This will help to add diversity back into the system and
hopefully help to keep the tank more vibrant. Detritus should
be removed regularly from the substrate to not only keep it
from becoming a nutrient sink, but also to allow the animals
living within it space to occupy. It may even be a good idea to
regularly remove some of this old substrate and replace it with
new. It is also now possible to add commercially raised
microfauna to the substrate to add to the diversity. All of
this may help to keep the diversity within the tank as high as

Not all older tanks have to necessarily go through old tank
syndrome. If the tank is properly maintained as outlined above
and few shortcuts are taken it is possible to have a tank look
as vibrant at ten years as it did at two. To most serious
hobbyists a tank does not even start reaching its peak until it
is at least two years of age. It is unfortunate and unnecessary
if we let our tanks pass through this level of optimum appeal
in a very short time.

  Advanced Aquarist

 Mike Paletta

  (3 articles)

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