IDzine01 wrote:
I don't think anyone would disagree that seeding a new tank with old
tank media is a fast and effective method of tank cycling. The fish
cycling vs. fishless cycling debate derives from cycling a tank from
scratch where fish are exposed to dangerous toxin levels. In this case,
fish often succumb to ammonia poisoning and those that do survive often
experience burned gills and compromised immune systems drastically
shortening their lives. The question that is presented is, is it ok to
kill or injure any fish for the purpose of cycling an aquarium?

Christie

Jim Morcombe wrote:

A couple of threads have made comments about cycling in a new tank that
I disagree with. For example, that it is impossible to cycle a new tank
without harming the fish and hence you must use "rubbish fish".

I have never lost a fish in cycling in a tank. Probably the main reason
is that I really understock the tank to start off with. Here's my method.

Most of the time I start a new tank is when my fish have just produced
their eggs so I have a couple of weeks notice in order to get ready. In
this case, I put an extra filter into one of my tanks and let it run
there so that is is full of bacteria. Sometimes I don't have this luxury.

I keep my fry in a net in the main tank for a couple of weeks. When I
am ready to give them their own tank, I take the dirty filter medium out
of one of the canister filters and rinse it out in the new tank. The
water turns into a murky grey/green soup. I then put the filter in the
tank and let it run for a couple of hours until the water is a little
clearer. I then dump the juvenilles into the new tank.

The "pond scum" from the canister filter settles all over the bottom of
the tank, making it pretty gross for the first couple of weeks. A lot
gets sucked into the filter, but far from all of it.

Thats it, the tank is now established. After a few water changes, most
of the pond scum has disappeared, but by then the bacteria is well
established in the tank.

With this method, I am putting in much more bacteria in the tank than is
needed for the tank, so the bacteria level will fall as the tank
establishes itself rather than building up.

When I set up a new tank at school for my science students, I often
don't get around to establishing the new filter first, but this doesn't
seem to make much difference. I make a party trick out of making the
water as murky as possible and then dumping a few fish in straight away.
The kids always accuse me of trying to kill the fish and are amazed
the next day to see the fish swimming around happily in much clearer
water. I then use this as a lead in to explaining the nitrogen cycle.

Note that although the bacteria level drops off, the algae in the pond
scum does not, so this does not add to the level of ammonia in the tank.


I think those that happily raise "feeder fish" would say "yes", while
those that run around the garden catching snails and mixing up prawn
jelly would say "no".