Fishkeeping Myths

Neale Monks explodes some of the most common fishkeeping myths.

As your career progresses, you’ll quickly learn that other fishkeepers are among the best sources of information. But not all ideas widely held are necessary scientifically accurate. Indeed, as Dr Neale Monks explains, some are downright wrong! Take these for example…

Fish grow to the size of their tank.
This is one of the oldest and most dangerous myths. While it is true that some types will become stunted when kept in overcrowded conditions, most do not.

Oscars, Tinfoil barbs, Silver dollars and plecs are examples of species that don’t become stunted and they shouldn’t be purchased unless you have sufficient tank space.

Goldfish and Clown loaches are among very few ornamental fish species that do become stunted. But does stunting cause harm? That’s difficult to answer, but fish in overcrowded conditions are going to be more prone to diseases caused by poor water quality and pH instability, such as finrot and fungus.

Aquarium plants are difficult to grow.
By the standards of plants we grow in our gardens, aquarium plants are weeds. Given sufficient light and the right substrate, most species will grow easily and rapidly. So why do aquarists often have trouble getting aquatic plants established?

Most of the time, beginners underestimate how much light their plants require. Plants make their food through photosynthesis and, without sufficient light, literally starve to death. Estimating how much light plants require can be tricky, but generally red plants need the most, pale green plants are fine with a little less and dark green plants often get by with the least.

In absolute terms, dark green plants like Java ferns, Anubias, Java moss and many Cryptocoryne species such as C. wendtii will be happy with around 2W of light per gallon of water. For most aquaria, that works out at two fluorescent lights running the length of the tank. These plants are also pretty indifferent about substrate and water chemistry and consequently make great choices for the less experienced aquarist.

By contrast, some plants sold in aquarium shops aren’t aquatic species at all. Why retailers offer them is a mystery, but, in any case, if the plant you’re looking at isn’t in your aquarium book or magazine – don’t buy it!

Whatever plants you opt for, maintenance is important. You’ll need to periodically add fertiliser to the aquarium, either as drops or pellets pushed into the substrate. The lights will need to be replaced after a certain length of time as well, typically 6-12 months depending on brand.

Choose lights optimised for plant growth. Some tubes are designed for other purposes and less useful. You’ll need to thin plants out every few weeks to prevent overcrowding and old leaves should be snipped once they start looking algae-ridden or ragged.

My aquarium needs a clean-up crew.
No freshwater aquarium needs one! In marine aquaria, this assortment of scavenging animals makes sense. They keep the sand turned over, remove uneaten food, and, if needs be, consume dead livestock without the aquarist needing to move delicate corals and other sessile invertebrates.

But cleaning up is easy in a freshwater aquarium. During water changes you can syphon out detritus without fear of damaging plants, and, if you must move the rocks or bogwood, it’s no big deal.

By all means buy catfish, loaches, shrimps or whatever as you wish, but don’t feel that you have to. Remember that every time you add an animal to an aquarium it gets dirtier, not cleaner.

Guppies are great fish for beginners.
Wild guppies are hardy and adaptable; for example they are able to live in seawater perfectly well. But fancy guppies of the types sold to aquarists are much less resilient and need to be pampered if to thrive.

When thrown into an immature or poorly maintained aquarium, fancy guppies are extremely prone to diseases such as finrot.

Even under the best conditions, fancy guppies don’t mix well with other species. The males are so encumbered by their long tail and dorsal fins that they are prime targets for fin-nipping fish such as some barbs and tetras. Even otherwise benign fish like angels and Upside-down catfish have been known to nibble.

Male guppies are notoriously aggressive towards one another and will also hassle any females that are kept with them, so keep guppies in large group with females outnumbering males by at least a ratio of 2:1.

Small water changes are best.
In the early days of the hobby, aquarists believed that ‘old water’ was somehow better for fish. Because old water contained a lot of nitrate and organic chemicals, it tended to become rather acidic. If you did a big water change and added water with a basic pH, you ran the risk of exposing the fish to a sudden and extreme pH change – something that could kill them.

It made sense to do small water changes instead, so that the fish could adjust to any slight changes in pH.
Modern day aquarists now understand that the more the water is changed, the better. Indeed, many fish simply won’t put up with old nitrate-rich water at all – cichlids, mollies and marine fish for example.

Weekly water changes of at least 25% will dilute the nitrate and organic chemicals that cause acidification in the aquarium, preventing that particular problem.

Big, regular water changes keep the aquarium much fresher than would otherwise be the case, meaning that your fish will be happier and healthier.

Undergravel filters are obsolete.
There’s nothing wrong with a good undergravel filter and, if your budget is limited, this type can make a very sound investment.

The reason people don’t use undergravel filters that often is because they have quite awkward limitations. To start with, undergravel filters are not compatible with most plants. Any plant with roots will find the oxygen-rich water flowing through the gravel very annoying. Growth rates will be limited, assuming the plant becomes established at all.

Undergravel filters also depend on the substrate being relatively uncluttered. A few plastic plants and the odd bit of bogwood won’t do any harm, but a huge mass of rocks that block the flow of water will create dead spots in the gravel where no filtration can take place.

To get the most from an undergravel filter you need to maximise the flow of water; for example by using multiple air stones or one or more powerheads.

Maintenance is also important and undergravel filters should be stirred every week or so, and any detritus syphoned out. Once a year it’s a good idea to take apart the tank and give the underside of the filter plate a clean as well, taking care to make sure the gravel stays cool and wet so that the bacteria aren’t stressed.

You should add a little salt to the aquarium.
There’s no real need. Salt doesn’t buffer pH or increase hardness, so the idea that it is beneficial to hardwater fish such as livebearers and Rift Valley cichlids is spurious. If keeping hardwater fish, you need to raise the carbonate hardness of the water using something like a Malawi salt mix or by adding crushed coral to the filter.

Does salt have therapeutic value? At doses of up to 3g/l, it can be used to treat a variety of ailments. It reduces the toxicity of nitrite and nitrate, and reduces the likelihood of secondary infections such as finrot and fungus. Similar doses can also be used to treat whitespot, particularly when coupled with increases in temperature. But, as a routine addition to the aquarium, salt is redundant and, over the long term, potentially harmful to fish that do not naturally come from brackish waters.

Predatory fish need live food.
Very few predatory fish need live food. It is a hassle, being expensive, inconvenient and potentially a way of introducing disease.

For the vast majority of predatory fish, wet frozen foods like bloodworms and krill make perfectly good staples. Larger fish will usually accept chopped or whole seafood as well. Newly imported fish may be reticent about accepting frozen foods, in which case live river shrimps, earthworms, mealworms, crickets or snails might be used, depending on the predatory fish in question.

All community fish can be kept together.
Labelling something as a ‘community fish’ means it will get along well with other fish of similar size. Since most big fish view small fish as potential prey, mixing species of dramatically different sizes is asking for trouble.

The classic examples are Angelfish and Neon tetras, both excellent community fish. But Angelfish are predators and large specimens will happily eat small fish, such as Neons. Other potentially predatory community fish include Giant danios, Pictus catfish and Asian killifish.

Hard, alkaline water isn’t much good for tropical fishkeeping.
Nothing could be further from the truth! Most aquarium fish don’t care too much what the precise pH is. What they don’t like are sudden changes. Carbonate hardness inhibits acidification, resulting in wonderfully stable water conditions.

The main problem with hard, alkaline water is that softwater fish don’t tend to spawn or breed successfully in it.

If you want to breed, your best bet is to concentrate on species that naturally prefer hardwater conditions. Livebearers, Tanganyikan and Malawian cichlids, Central American cichlids and brackish water fish would all make good choices.

There’s so much to learn!
Fishkeeping can be as simple or as complex as you make it. If you want to keep things simple, start with a reasonably large tank, as small tanks are notoriously fiddly to keep healthy. A 90-150 l/20-33 gal system is ideal.

Use a fishless cycling method to mature the tank and then choose a few fish suited to your local water conditions.

If you live in a hardwater area for example, livebearers would be ideal. Make sure you research diet, social behaviour and maximum size carefully before purchase. Do 25-50% water changes weekly without fail and keep on top of filter maintenance as well. That’s basically it!

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