Is an Ounce of
a Pound of Cure?
Many of the professional aquarists I’ve
talked to over the years go a step further,
routinely medicating quarantined fish for a
host of diseases, even if there’s no evidence
those diseases are present. Some also give
new freshwater fish a salt dip, and new
marine fish a freshwater dip, to kill off
parasites before placing them in quarantine.
But that’s not something most home
aquarists should be doing for several
reasons, and Miller-Morgan and Noga agree.
First, both pointed out that professionals
usually use medications based on an in-depth knowledge of both the species they’re
dealing with and the kind of pathogens that
species is prone to; they also understand the
impact of medications on both organisms.
Home aquarists, however, rarely have that
kind of knowledge.
In addition, adding medications to tank
water is in itself a stressor to fish because
it changes the concentration of dissolved
solids in the water, which in turn affects the
fish’s osmoregulatory processes.
And lastly, said Miller-Morgan, treating
for diseases the fish may not have can
ultimately lead to medication-resistant
pathogens, which can create a much bigger
problem down the line.
So what would a good quarantine system
look like? The size of the tank will vary
according to the sorts of fish you keep—
larger or fast-swimming fish, for instance,
require larger quarantine tanks than smaller,
quieter fish. But beyond that, simpler is
better; keep the lighting low—it keeps fish
calmer—and make sure that anything you
put into the tank is easily sterilized.
That means opting for things like plastic
plants and PVC pipe (added not to make
the tank look beautiful, but to make
the fish feel secure) over real or silk
plants. “And nothing porous, like lava
rock, because pathogens can get into
the pores,” Miller-Morgan said. He also
recommends skipping the substrate, since
a barebottom tank is easier to keep clean
and also to sterilize later. And, he adds,
make sure that any nets and siphons used
in a quarantine system are kept separate;
using them in an established tank is a
good way to spread pathogens.
The only “problem” that has to be
addressed with any tank that isn’t in
constant use is how to keep the biofilter
going. Some people keep a few fish in
them, transferring them to their main
tank when the quarantine tank is
needed for new arrivals. You can also
keep the biofilters running in a fish-free
quarantine tank by adding small amounts
Personally, I keep my quarantine tanks
empty between use; when I need them, I
instant-cycle them by pulling filter pads
from my established tanks and putting
them into the quarantine-tank filters.
(Alternatively, you can keep an extra
box filter running in an established
tank, ready to move to a quarantine
tank when needed.)
If you need to sterilize a quarantine
tank, Miller-Morgan says that bleach, at a
concentration of 200 ppm (or 200 mg/liter
of water), will do a great job. However, he
cautions, organics do cause bleach to break
down, so make sure you rinse everything
thoroughly before using the bleach, or it
won’t be as effective.
Back to the Beginning
To close this month’s column, I thought
I’d return to the saga of my nephew and his
I’d like to be able to tell you that Aunt
Laura’s wisdom prevailed that evening at
the fair, and that I managed to talk him
(or rather, his parents) into stopping at the
local pet shop for a quarantine tank on the
way home. I did not.
Rather, the fish went directly into
my nephew’s 30-gallon goldfish tank
along with his three established fish
(although I did manage to work in a
lesson on acclimation techniques). I did,
however, suggest to my brother that he
do a series of partial water changes over
the course of the next week to reduce
any free-swimming parasites that might
be in the water.
As I write this, several weeks have
passed and so far neither the new fish
nor the originals are showing any signs
of a problem. So my nephew could well
But I also know that good luck rarely
lasts forever, and if Ben is serious about
fishkeeping, which he seems to be, there
will be many finned additions to his
collection in the years to come.
So I’ve been thinking: His birthday is
coming up. Wouldn’t a quarantine tank
make a perfect gift?