52 How Many Fish Can Be Added?
Description
This article is from the Beginning Fishkeeping FAQ, by Thomas Narten with numerous contributions by others.
52 How Many Fish Can Be Added?
The easiest answer to that question is ``one fish at a time.'' As far
as how many in total can safely survive, a frequently used
rule-of-thumb is ``up to a maximum of 1 inch of fish per gallon.''
Much discussion of this rule has suggested that it really should read
``up to a maximum of 1 inch of SLIM-BODIED fish per gallon.''
``Slim-bodied'' could be fish such as neon tetras, White Cloud
Mountain Minnows, danios etc.; ``medium bodied'' might be red-tailed
black sharks, tiger barbs, platys, cory cats etc.; ``heavy bodied''
would be goldfish, oscars etc.
In other words, this is only a rule of thumb, and the ``maximum''
population that is safe and humane will vary from tank to tank.
Factors that increase your possible fish load include:
* regular and significant water changes,
* HEALTHY live plants, and
* more than one type of well-tended filtration (remember to think of
your filter as alive; it needs care just as do your fish).
Likewise, factors that decrease your possible load include:
* erratic or sparse water changes,
* no plants or UNhealthy live plants, and
* limited or ill-tended filtration (an undergravel filter can do a
great job, but if it fails for some reason and was the only
filtration on the tank, a heavily stocked tank will experience
much more disastrous consequences than one with a light load).
So, back to adding fish. Often it is not practical to add fish one at
a time - for instance, you find some especially great looking neons
and want to add a small school (6 or 7 fish) to your recently cycled
20 gallon tank. You currently have one 2-inch pl*co and three 1.5-inch
platys. Adding the neons will essentially double the ``volume'' of
fish in the tank. In this case, you will see the same effects as
cycling your tank, i.e., an ammonia and nitrite spike before the
bacteria grows to match the new fish population. Test your water
frequently and be prepared to do emergency partial water changes if
the ammonia levels go up too far.
The bio-filter for your tank is only ``fed'' by the wastes of the fish
you have in the tank. This means that no matter how large your filter
(e.g., one rated for a fully stocked 50 gal tank on your 20 gal), the
bacteria population will be limited by the ``food'' it has. Few fish =
small bacteria population.
We are accustomed to thinking of bacteria reproduction as
``explosive''. Many bacteria can double their population size in
hours, after all... but as we have seen in the CYCLING SECTION, the
appropriate nitrifying bacteria are relatively slow to reproduce.
There will be a time delay between the increased waste production of
additional fish, and increased waste processing by the bacteria. In
extreme cases, the ammonia increase could harm or kill your fish
before the bacteria population had time to ``catch up'' to the amount
of available nitrogenous wastes.
This is why it is wise to add fish slowly and gradually. Safely
bringing your tank's population up to the maximum load can take more
than 6 months; in fact, it should be permitted to take at least that
long. Leave breaking the rules to those with more years experience
than they have fish.
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