Skepticism in the Aquarium Store, Part 1

Earlier this year, I gave a presentation at Ottawa Skepticamp 2013 titled “Skepticism in the Aquarium Store.”  It definitely got some smiles out of people, not least the radio host who interviewed one of the organizers about Skepticamp and spied the unusual title.  My presentation took the axiom that skepticism is vital to virtually every human endeavor and brought it to one of my dearest hobbies: aquarium keeping.  And now I’m bringing that to you.

I like fish.  Fish provide a truly astounding variety of shapes, sizes, and behaviors to observe, comparable only to insects.  Their diversity puts more conventional pets to shame, and they have the added perks of being confined to specific places in people’s homes, being hypoallergenic, and providing relaxing waterfall background noise.  There’s an artistic and collection-building aspect to fishkeeping that isn’t present with other pets, which appeals to me.

One other thing that differentiates fishkeeping from many other pet-related hobbies is that there isn’t really a fishy equivalent to a dog rescue.  Sure, one can pick through Craigslist and Kijiji for people giving away their kits or their animals, but that’s a time-consuming and risky method.  For better or for worse, fishkeepers are stuck with pet stores, and that means getting stuck with a lot of bad advice.  Like car dealers and the slimy cads who sell people fancy audio cables, the underpaid and often unprepared sales associates who staff the fish section often have priorities other than the best life for their livestock.

Aquakeeping, like car sales, treating disease, and politics, is an endeavor that requires a little background and a lot of…skepticism.  And it starts right at the beginning.

Picking Your Tank

I’m going to say this once, loud and clear: NO FISHBOWLS.

Fish have diverse needs, but one thing they all have in common is that they depend on oxygen that dissolves into their water from the surface.  The rate of that dissolution is based in part on the surface area of the tank.  ANY vessel that is narrower at the top than elsewhere ends up with less oxygen than a similar rectangular vessel.  Add to that the difficulty of finding filters and other equipment that can deal with an unusual shape, and it’s clear that one is better off with a standard, “boring,” rectangular prism.

(There are some situations that require other shapes.  Skilled aquarists who keep sea jellies, for example, do so in tanks without corners.  But that’s another story.)

Buying Fish Right Away

It used to be common for pet stores to try to sell people fish the same day that they bought their tanks.  With the advent of generous return policies at most pet stores, this is rarer now.  And thankfully so, since buying fish right away is a terrible idea.

The vast majority of people who keep fish do so in tap water that they’ve treated with some sort of chelator to remove the chlorine and chloramine.  Water companies don’t put that stuff in water because it causes lethal osmotic shock in fish—they put it there because it kills bacteria.  And one thing entirely too few aspiring aquarists, especially the “my kid just turned 10 but we can’t afford a dog” kind, know is that some of those bacteria are absolutely vital to the success of an aquarium. Most fish excrete ammonia as their primary waste product.

Ammonia, as those of us who have cleaned floors or windows know, is not a friendly substance.  In a natural setting, the Nitrosomonas bacteria that feed on ammonia would already be present in abundance, growing on any available surface area and keeping ammonia levels down.  But in an aquarium, chances are that any bacteria present in the system begin at extremely low populations.  Until then, any fish in the tank are dumping ammonia into the system faster than the bacteria can eat it, and it’s a gruesome race to see whether the bacteria will grow quickly enough to keep the ammonia below the point where the fish can no longer cope.

Depending on how densely the naïve aquarist packed their brand-new tank, the resulting scene might look like $10 flushed down the toilet, or it might look like one of those eutrophication-induced Biblical plagues.  But sometimes, a few fish survive, shocked and poisoned but still alive.

Those will next be subjected to Nitrosomonas’s leavings, in the form of nitrite salts.  Nitrite is less toxic than ammonia, but still unpleasant in large quantities, especially to fish that are still recovering from ammonia toxicity.  So the race begins again, between the remaining fish’s nitrite tolerance and the next set of bacteria, Nitrospira and Nitrobacter, which turn nitrite into (mostly) harmless nitrate.

This tragic sequence is known as “new tank syndrome,” and it costs our hobby numerous new practitioners every year.  Almost every ad for someone getting rid of an aquarium kit without fish is a story of naively buying kit and fish at once and not knowing that the system needs to equilibrate before fish are safe in it.

So how does one escape this seemingly inevitable problem?  That’s called “cycling the tank,” and aquarium handbooks are abuzz with ideas, as is the Internet.  The short version is that the bacteria have to be cultivated before fish are safe, and there are a lot of ways to do that.  And all of them involve not buying your full set of fish the same day you come home with a brand new glass box and some filters.  Patience, young Padawan.


So you’ve avoided New Tank Syndrome.  What happens next?  Do you just put in as many fish as you like?  The dealer’s tanks are jam-packed, and surely they know what they’re doing.

Well, yes they do.  What they’re doing is maintaining a pet store.  Their system is designed to house large numbers of fish more-or-less safely for relatively short periods, and to tolerate losses that would make most pet owners cringe.  A home system doesn’t have the kind of monstrous, water-heater-sized filter that a pet store might use, and is hopefully interested in the long-term happiness of its charges.

So the short answer is, you’ll have to stop well before they do.  A good rule of thumb that I picked up in the United States is “one inch of fish per gallon.”  So if you have a 10 gallon starter kit, you might get 8 or 9 neon tetras (~1 inch, or slightly larger), or a few platies (~2 in), or some platies and some Corydoras catfish, but you won’t get all of that—not without crowding your system well past what an ordinary filter could maintain.

This rule is great, but it’s also limited.  It’s a rough measure of how much oxygen a fish needs and how much waste it produces, not a hard-and-fast determinant.  Some fish, such as particularly sedentary catfish or anything with an accessory breathing organ, take up fewer fish-inches than their size would imply.  Other fish, such as anything deep-bodied or above about four inches in length, take up more.  Goldfish are a classic example: because they are much bulkier than most other aquarium fish and produce way more waste, they take up roughly four times the fish-inches another fish of their size would require, and also get bigger than many people realize when their needs are met.  (Still thinking about that fishbowl?)  So stocking a tank requires a measure of discipline, and ideally some sort of plan.  (More on that later.)

Sloppy Work

So once you’ve set everything up, it’s all smooth sailing, right?

Come on.  You know better than that.

Now you’ve got to feed your new pets, and change their water periodically, and clean their filter.  (That filter is mostly there as a home for the bacteria, by the way.)  But if you don’t, that’s okay too.  If you’ve already gotten them past the cycling phase, they’ll probably survive, even if you overfeed them to the point that leftovers hang around for days.

But now you’ve got snails.  They probably came in with a plant, and with all that leftover food around, they’re multiplying.  By the time you see them, there are probably at least ten times as many snails as fish in your tank, but you might not mind, because you also have an algae problem that’s starting to make the inside of your tank hard to see.  So you buy a pleco catfish, or some sort of snail-eating loach, to perform some pest control.

And it dies within 24 hours.

You exchange it for another one at the pet store, and that one also dies during the night.

At some point you figure out that your water is extremely dirty, and you do a wholesale cleaning, right down to scrubbing the glass.  Then, all of your old fish die.

What non-Euclidian hell have your fish led you into?  The hell of Zombie Tank Syndrome.

By not keeping the tank clean, and in particular by overfeeding it, you caused the water conditions to slowly deteriorate.  The snails and algae, like roaches in a house, are signs of that excess.  But your fish, except maybe a few sensitive individuals, could slowly acclimate to the worse conditions.  A new fish, however, coming from clean dealer water, can’t adjust to the cesspool quickly enough, and goes into shock within a few hours.  That’s usually when people realize that something is wrong, and clean their water.  But once the water is this dirty, the existing fish need to be eased out of it, or they’ll go into the opposite kind of shock.  Hence, Zombie Tank, and a lot of garage sales.

An aquarium is a hybrid system.  Some of it maintains itself, but for other parts, humans are the organ that keeps everything balanced.  Only in the most impossibly large systems can a human role in keeping an aquarium in order be somewhat avoided, and even that is unlikely.  So it’s vital to control what goes in (food and oxygen) and deal carefully with what goes out (waste via bacteria).  Live plants are very helpful in this respect, in that they consume the same nutrients that cause algal blooms.

Next Time


I’ll be visiting fish-keeping again two more times, to go over the entertaining, involved, and sometimes tricky process of selecting the fish that go in one’s tank.  Until then, dear readers.


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