1. The tank: 20 gallons for the first fish
The number to remember is 20 gallons for your first goldfish, and about 10 more
for each one after that. For the big single-tail kinds (comets, commons) even
that's on the small side once they grow up; those really want 30 or more each, or a
pond.
Why so big? Three reasons. First, goldfish get big. Not "big for a fish in a bowl."
Big. A fancy goldfish grows to 6 or 8 inches, and a comet can pass a foot. Second,
they are the messiest fish in the hobby: they eat a lot, they have no real stomach,
and it all goes straight through. Third, and this is the real one, more water means
that all that waste is more diluted, so the poisons I'll explain in a minute build
up slower and you have more room for error.
A 20-gallon "long" tank and a 20-gallon "high" tank hold the same water; get the long
one, goldfish like swimming room more than depth. Put it on something that can hold
it: water is about 8.3 pounds a gallon, so a full 20 with gravel is close to 200
pounds. Not the card table.
No heater. Goldfish are cold-water fish and are happiest somewhere in the 60s to low
70s Fahrenheit, which is to say normal room temperature. This is why they don't go
in with tropical fish (see below).
2. A filter, and a bigger one than the box says
Because of the mess, you want a filter rated for a tank bigger than the one
you have. For a 20-gallon goldfish tank I'd get a hang-on-the-back power filter
rated for 30 or 40 gallons, or two smaller ones. The filter does two jobs: it
strains out the floating gunk (mechanical), and, much more important, it gives the
good bacteria a place to live (biological). Which brings us to the single most
important thing on this page.
3. The nitrogen cycle (read this one twice)
Here's what actually kills most goldfish, and it's invisible:
- Fish waste and uneaten food break down into ammonia. Ammonia is
poisonous to fish, even at levels you can't see or smell. In a bowl with no filter
it builds up in a day or two. The fish gasps at the top, its fins get ragged, and it
dies "for no reason."
- In a filtered tank, a kind of bacteria grows on the filter media and gravel
that eats ammonia and turns it into nitrite. Nitrite is also
poisonous.
- Then a second kind of bacteria grows that eats the nitrite and turns it into
nitrate. Nitrate is only mildly harmful, and you get rid of it with water
changes.
Getting those two bacteria colonies established is called cycling the tank,
and it takes roughly four to six weeks from the day you first add fish. During
that time the ammonia spikes, then the nitrite spikes, then both fall to zero and
nitrate starts creeping up. That's a cycled tank. Until then, your fish is living
through a chemistry experiment, and here is how you get it through:
- Start with one fish, not three.
- Buy a test kit for ammonia and nitrite. The liquid drop kind is more
accurate than the paper strips. It's the best ten or fifteen dollars you will spend.
- Test every day or two. Any time ammonia or nitrite reads above zero, change
some water (a quarter to a third) to bring it down.
- Feed lightly.
- Do not change or rinse out the filter cartridge during this time. That's
where the bacteria are living. When you do eventually clean it, swish it in a bucket
of old tank water, never under the tap; chlorine kills the bacteria and you start
over.
Once ammonia and nitrite both read zero for a week and nitrate is showing up, you're
cycled, and from then on the tank mostly takes care of the poison for you. Every
goldfish that "died a week after we got it" died of ammonia in an uncycled bowl.
Every one.
4. Water changes: the whole secret
Even in a cycled tank, nitrate builds up, along with other stuff the filter can't
touch. So you take out some old water and put in new. About 25 to 30 percent,
once a week. That's it. That's the whole secret to a fish that lives fifteen
years.
- Get a gravel vacuum (a siphon tube with a wide end). You stick the wide end in
the gravel, the dirt gets sucked up with the water, and you're cleaning the gravel
and changing water in one step. Five minutes for a 20-gallon.
- New water gets a dechlorinator (water conditioner) before it goes in.
Tap water has chlorine, and a lot of cities now use chloramine, which doesn't gas
off if you just let it sit. A few drops of conditioner, done.
- Match the temperature roughly to the tank. Room temperature tap is fine.
- Never tear the whole tank down and scrub everything. I know your mother
did it that way. That's killing the bacteria and starting the cycle over every
month. Partial changes only.
5. Feeding: less than you think
A goldfish will act like it's starving every time you walk past. It is lying.
Overfeeding is the second biggest goldfish killer after the bowl, because uneaten
food rots into ammonia and because a fish stuffed with dry flakes gets bloated.
- Once or twice a day, only what they finish in a minute or two. If food is
lying on the gravel, you gave too much.
- A good sinking pellet is better than flakes for fancies, because gulping at the
surface for flakes makes them swallow air and float funny.
- Give them vegetables. Shelled peas (frozen, thawed, squeeze the skin off, mash a
bit) once a week or so keep them regular. Blanched zucchini and lettuce too.
- Skipping a day now and then does them no harm at all. A healthy goldfish can go
a week without food when you're on vacation; that's far safer than a neighbor
dumping in half a can.
6. Fancy vs. comet: they're different animals
All goldfish are the same species, but a few hundred years of breeding has made two
very different groups:
| Single-tails (common, comet, shubunkin) |
Fancies (fantail, ryukin, oranda, black moor, telescope, and so on) |
| Long, streamlined body, one flat tail. The "feeder" fish and the carnival fish are
these. Fast, tough, and they get big: 10 to 14 inches is normal for a comet with room to grow. Really a pond
fish. If you keep one indoors, think 30 gallons and up, and a long tank. Bubba is a comet. |
Round egg-shaped body, double tail, sometimes a wen (the raspberry-looking cap on
an oranda) or telescope eyes. Slower, clumsier, stay smaller (6 to 8 inches). All those insides are squeezed into a
round body, so they're prone to swim bladder trouble (floating upside down after a big meal). Better indoor fish,
but need the same water quality. Don't put them with single-tails, who will eat all the food before a ryukin gets
across the tank. |
7. Tank mates: mostly, other goldfish
- Not tropical fish. Tropicals want water in the high 70s; goldfish want it
cooler. Somebody's unhappy no matter what you set the heater to. Plus goldfish will
eventually eat anything that fits in their mouths, and a neon tetra fits.
- Not a betta. Different temperature, and one of them will end up
picking on the other.
- Not a "sucker fish" (plecostomus). A common pleco is a tropical fish
that gets over a foot long, and they have a known bad habit of latching onto the
slimy sides of slow goldfish. I've seen the damage. No.
- Other goldfish of the same type are the best tank mates. Fancies with
fancies, single-tails with single-tails. Snails are fine if you want cleanup.
White cloud minnows tolerate cool water and are too quick to get eaten, if you must
have something small.
8. When they get sick
I'm not a vet, so this is general. But nine times out of ten, a sick goldfish is a
water-quality problem wearing a disguise. The first thing to do for any sick
fish is test the water and do a water change. Then:
- Ich (little white spots like salt grains, fish flashing and rubbing
against things): a parasite. Very common, very treatable if caught early, with the
standard ich medicine from the pet store and by raising the temperature a bit. Follow
the package.
- Fin rot (fins look ragged, edges turning milky or red): a bacterial
infection, and almost always from bad water. Clean water usually fixes it; an
antibacterial treatment if it doesn't.
- Fungus (white cotton-looking fuzz, usually on an injury): treatable with
a fungus medication; keep the water clean.
- Floating or sinking, can't stay level (mostly fancies): usually
constipation or gulped air, not a disease at all. Skip feeding for two days, then
peas. Most of the time it clears up.
- Gasping at the surface, clamped fins, red streaks in fins: ammonia or
nitrite poisoning. Water change NOW, then test, then another water change.
A ten-dollar plastic tub makes a fine quarantine or hospital tank so you're not
medicating your whole main tank. And new fish go in quarantine for a couple of weeks
before they meet your old fish. That rule cost me a whole tank of fish to learn in
1993, so please take it for free.
9. Goldfish myths, corrected
| "A goldfish only lives a year or two." |
A goldfish in decent water lives 10 to 15 years easily, and there are well-documented ones past 30. The year-or-two
fish was killed by the bowl. |
| "It only grows to the size of its tank." |
What actually happens is the fish is stunted by poor water and stops growing on the outside while its organs keep
growing. That's not "staying small." That's being slowly crippled. Given room and clean water, the fish grows. |
| "Goldfish have a three-second memory." |
Nonsense. Bubba knows what time dinner is, knows the difference between me and a stranger, and learned to nudge a
ping-pong ball in about two weeks. Goldfish can be trained to swim through hoops. They remember for months. |
| "They don't need a filter, just change the water." |
See the nitrogen cycle. Without a filter for the bacteria to live on, you'd have to change most of the water every
day or two forever, and even then the fish is getting dosed with ammonia in between. |
| "Feeder goldfish are a different, cheaper kind." |
They're ordinary common and comet goldfish, raised in crowded tanks. Bubba was a 15-cent feeder. Give one a
real tank and see what it turns into. |
| "Tapping the glass gets their attention." |
It does, the way a fire alarm gets yours. Sound carries hard through water. Don't. |
| "You can tell it's happy because it's swimming around." |
A goldfish frantically pacing the glass or hanging at the top is often a fish in bad water. A happy goldfish
cruises the whole tank, roots in the gravel, and comes to see you. |
| "They'll be fine in the bowl until we get a tank." |
Then please get the tank this week. Until then: change half the water in the bowl every single day, with
dechlorinator, and feed almost nothing. |
10. Meet Bubba (and the rest)
Bubba - comet, orange with a white belly, hatched sometime in 1990 as far as I
can figure. Came home from the pet store in a bag with a dozen others meant to be
turtle food; the turtle wasn't interested in him, and neither was I, at first. Nine
years later he is eight inches from nose to tail and the boss of a 55-gallon tank.
He eats out of my fingers and he has a thing about the gravel vacuum: he follows it
around the tank the whole time like it's a lawn mower and he's a dog.
Shorty - shubunkin, blue-gray with orange and black speckles, about six years,
Bubba's tank mate. Fast. Steals food.
The fancy tank - a separate 30-gallon with two orandas (Mabel and Louise, red
caps, four years old) and one black moor (Ink) who bumps into things because
telescope-eyed fish can't see well. That's normal for the breed; you just don't put
sharp decorations in with them.
Setup: 55-gallon, two hang-on filters rated for 60 gallons each, bare-ish
gravel, a couple of big smooth rocks, plastic plants (Bubba eats real ones), no
heater, a 30-percent water change every Sunday morning while the coffee's on. Ammonia
0, nitrite 0, nitrate stays under 20. That's the whole routine, eleven years running.
Pictures: I have an old Polaroid of Bubba at two inches and one from this summer
that I need to get scanned. The guy at work with the scanner has been "getting to
it" since June. 
More fish pages
The Reef Tank Page - Brian's saltwater tank. The opposite end of the hobby from mine
(and about ten times the money), but he's serious about water quality too.
Mr. Whiskers' Cat Emporium - Homepage of the Month. Keep the cats away from the tank.
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GOLDFISH DONE RIGHT
since January 1999. Please go change some water.
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