6 Basic Mistakes of the Novice Aquarist

Featured Article

Issue: December 2014

Author: Radek Bednarczuk

Photographer: Radek Bednarczuk

A dedicated fishkeeper reviews some common mistakes first-time fishkeepers make, and gives some advice to reduce the risk of livestock losses in a starter aquarium.

I’ve been involved in the freshwater aquarium hobby for a few dozen years—with some short breaks— and in all this time I have come across many strange, glaring mistakes that first-time fishkeepers often make. Though it is far from a comprehensive list, here are some of those mistakes —and ways to avoid them.

1. No Biological Filtration

Novice fishkeepers often forget to provide biological filtration. During the initial buying spree at a pet shop they purchase an airstone and a pump, firmly believing that it will suffice. That might be true in a heavily planted tank with a deep substrate (which the nitrifying bacteria can colonize), low stocking levels, and a conservative feeding regimen; such a setup might cope with biological decomposition and transformation of nitrogen compounds (by nitrifying bacteria). However, even in such a tank, this equilibrium can easily be disrupted; sometimes all it takes it the addition of a new fish or an increase in feeding for a disaster to strike—and you’ll find your fish floating belly-up as a result of a sudden ammonia or nitrite spike.

Even a small aquarium should be equipped with a biological filter, either internal or the hang-on-back type, while a bigger tank should have an external filter (i.e., a canister containing biofiltration media or a trickle filter). The filter should be chosen with both the aquarium volume and the future stocking levels in mind. Remember, the air pump is merely an addition. Inside the filter there should be enough media (ideally lava rock or an equally porous substitute) to support colonies of beneficial bacteria capable of breaking down harmful waste products—that is, converting ammonia to nitrite, and the latter to the much less toxic nitrate.

While cleaning the biological medium or media (which should not be done too often) remember to use aquarium water (obtained, for instance, by being siphoned off into a bucket), not tap water, which is often chlorinated. Thus you will avoid destroying/ reducing the population of bacteria living on the lava rock, sponge, etc., of the biological filter. Here we come to another problem. When people finally decide to buy a filter, they often consider it a way to avoid the most dreaded chore of aquarium keeping: regular partial water changes. They couldn’t be more wrong.

The final product of the nitrogen cycle, nitrates, must also be removed. They can stunt our fishes’ growth and cause reproductive difficulties. This is especially important when the stocking level is high, plants are scarce (or absent), and the fish have high metabolism rates (e.g., cichlids). Some hobbyists use hydroponic or denitrifying filters. In such a case, water changes can be less frequent.

2. Incorrect Feeding

You should bear in mind that not all fishes will eat the same things. I once met a beginner aquarist who fed his fish bread, pasta, and sometimes even potatoes; hopefully, though, that was an extreme case. Different fishes have different diets; some of them are herbivores, others are carnivores, and still others are omnivores. That is why the food you use should be adapted to the needs of the fishes you own. While we are on the subject, another common beginner’s mistake is overfeeding.

Food is typically given a few times a day, in large amounts. In their natural environment fishes eat infrequently and they don’t have access to the rich (nutritionally dense) foods, abundant in vitamins, proteins, and fats, offered by the average aquarist. In short, your charges will simply get fat if they are fed this way.

Aquarium fishes should be fed infrequently, in small amounts, and fasted for a day every week. Young specimens ought to eat more often, while some mature fishes can even receive their food once every few days. Rest assured that your pets will not perish from starvation if you happen to skip a feeding!

3. Improper Stocking

Another commonly made mistake is combining randomly chosen species from various biotopes. In one such aquarium I saw fishes from almost every biotope, one from each of them. There was a piranha, a Tropheus, a goldfish, a betta, an angelfish, and a neon tetra. Yes, they all lived in the same tank! Before you start buying fishes, you should first educate yourself. Where do they live, how big do they grow, are they peaceful or aggressive, do they live alone or in groups, what physical and chemical parameters should be provided (temperature, pH, hardness)? You shouldn’t house species from different biotopes together because it would be impossible to provide optimal conditions for them all. The Earth is huge, and fishes from various corners of the globe cannot all co-exist. Some species from different biotopes can be kept in the same tank—but that is a subject for a separate article.

While we are on the subject of choosing fishes, another common new owner’s mistake is overstocking. The typical beginner would love to have all the fishes from the local pet shop in his or her tank. Repeated purchases (usually made every other day) are a common sign that you’ve got the fishkeeping bug (to make you feel better, I can tell you that everybody has done the same). However, do remember that your aquarium is not made of rubber. Research the minimum space requirements of any species before purchasing it.

4. Accidental Poisoning

One strange habit I have come across is turning off the filter for the night. In one case of this sort, the aquarium was located in the hobbyist’s bedroom and the noise interfered with sleep; another hobbyist simply wanted to save electricity. Unfortunately, when a filter is turned off, the bacteria inside it begin to die off from lack of oxygen and anaerobic decay sets in. When the filter is turned on again in the morning, your fishes are treated to a dose of toxic substances (such as hydrogen sulfide). As a result, the younger, weaker, or more sensitive specimens may be poisoned, sometimes fatally. The filter should be on 24/7, not unlike a fridge. In the event of a prolonged power outage, the filter should be cleaned thoroughly and seeded anew with nitrifying bacteria.

5. Using Too Many Chemicals for No Good Reason

Another common mistake of the beginning aquarist is the overuse of chemicals to combat diseases, usually by administering one drug that is supposed to treat them all, or by using various “miracle” additives/water treatments.

Where fish diseases are concerned, there are only a few ailments that a novice can hope to diagnose, such as ich and fungal infections (and even the former can be confused with velvet by the inexperienced). Identifying other diseases requires not only many years of practice, but also specialized equipment and a knowledge of fish pathology.

As for various algicides, they’re usually not necessary. In most cases you can control an algae outbreak by darkening the tank for about a week, changing two thirds of the water, then shortening the lighting cycle, lowering the stocking level, and reducing feeding. Adding more plants and introducing algae-eating fishes, such as loricariids, will also help make your algae problem go away. Chemicals are not always necessary.

You should also remember not to place the aquarium in the immediate vicinity of a window as direct sunlight can cause severe algal outbreaks. With regard to water treatments, nitrifying bacteria in liquid or tablet form can be useful at start-up time for the aquarium if you do not have a fishkeeper friend who could give you some media from a mature filter to put into your filter. That filter media material is basically all you need (unless your heart is set on a planted tank, in which case some fertilizers might also be required).

6. Lack of Patience (the Aquarist’s Prime Virtue)

Another new owner’s mistake is putting newly purchased fish into a tank filled with fresh tap water, devoid of beneficial bacteria responsible for the nitrogen cycle. Even worse, the water may be chlorinated. In that case, the weaker, smaller, or younger specimens will soon show frayed (burned) fins (pectoral and caudal). Should the gills be damaged as well, the consequences are usually fatal. Furthermore, without thegood bacteria, the water will soon turn milky/cloudy (protozoan bloom) and is likely to stink. When that happens, the inexperienced fishkeeper usually performs a large water change—putting even more fresh tap water into the aquarium—and the situation repeats itself.

As I wrote at the beginning, biological filtration is the basis of biological equilibrium in the aquarium. A newly setup tank lacks the microorganisms that convert harmful substances (ammonia, nitrite) into less toxic nitrate. To hasten the cycling process, you can add ready-made nitrifying bacteria cultures to the water and the filter itself; sometimes food for the microbes should also be added (unless it was included in the package). This could be any organic matter (for instance, a piece of frozen fish food), or you might add a few big snails (for instance, Ampullaria) to the aquarium.

Apart from the biological filtration, the tank should also be well aerated (using a diffuser, spray bar, or airstone). After two weeks on the average (or, even better, four) you can begin successively adding fishes to your aquarium; do test the levels of nitrogen compounds before you start, however! Once the fishes are in the tank you should feed them very sparingly for a week or two, for the bacteria can still be in short supply and they might struggle to deal with the metabolites. To be on the safe side, it is advisable to check the levels of nitrogen compounds once every few days.


There are surely many other beginners’ mistakes I have failed to include, but the ones listed here are the most important. Hopefully this article will help those readers who are only just embarking on their adventure with this wonderful hobby so that they do not get discouraged at the very beginning.

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