Aquarium with fish

Debunking the Top 10 Fishkeeping Myths


Do you know how many inches of fish a 10-gallon tank can hold? How about the recommended percentage of water to replace when doing a water change? Do you know how important it is to get the pH just right?

I have kept aquariums for years, and I thought I knew the answers to all these questions.  After all, the answers to these questions have been widely publicized since I first started keeping aquariums.

You may be as surprised as I was to discover that a lot of what has been accepted as basic facts in aquarium keeping are actually myths. In this article, you will discover the truth behind the many popular myths about fish keeping.

Myth 1: pH is extremely important 

It’s common for aquarium guides to give a recommended pH range for a specific fish species. In truth, most fish do well in a pH range that is a lot wider than indicated. What this means is that pH is no big deal in most cases.

Even rapid pH changes are not normally harmful to fish. Most fish species will do well. Although the preferred pH range is 6.5-8.5 for most fish species, they usually do well in a pH range of 5-9.

Even more surprising for me was when I found out that pH is not even as big an issue as we might think! What really affects fish has to do with the amount of the total dissolved solids (TDS) in the water, for example, salt. It just so happens that low TDS is accompanied by a low pH, so when the pH is below 5.0, this means the TDS is also 5.0, making the water unhealthy for fish.

Myth 2: Fish only grow to the size of the tank.

The idea that fish only grow to the size of the tank is based on a misunderstanding. It comes from a lack of knowledge of their care requirements.

A fish that has grown to their tank size is a fish whose growth was stunted. The tank size prevented it from achieving its full size. This restriction on its growth can also affect its health. As with other cold-blooded animals, fish grow throughout their lives.

For a fish to attain its natural size and to thrive, it needs:

  • A large enough aquarium.
  • A proper diet.
  • The correct water conditions.
  • The needed tank décor.
  • The appropriate tank mates if it is a social species.

Myth 3: Beginners should start with a small tank

This myth may seem like common sense. If you’re a newbie to fishkeeping, you should start off with a five-gallon aquarium or even a smaller size, right?

Wrong! This myth is an example where common sense is based on a lack of understanding.

Small aquariums should only be kept by those who are seasoned aquarists. Why? The smaller the aquarium, the less stable it will be. It’s actually more difficult to maintain the water quality in smaller aquariums vs. larger ones.

Because of this, smaller aquariums require greater maintenance, and you have less room for error. The recommended size for a starter tank is between 15-30 gallons.

Myth 4: You don’t have to do water changes if you have a filter

A filter in your tank will help keep the water clean, but it’s not enough. The purpose of water changes is to keep the nitrates in the tank (NO3) at a safe level (20 ppm in freshwater tanks). A filter alone cannot handle this job.

Myth 5: You should do a 25% water change once a week

This guideline is frequently seen in the literature, as are variations of it. The problem with this myth is that it misses the point of water changes. The purpose of water changes is to keep the nitrate in the water at a safe level (20 ppm).

If a 25% water change does not keep the nitrate levels at 20 ppm, then you would need to do water changes more frequently than once a week. Conversely, if nitrates are not produced in large amounts, you may be able to get away with doing a water change only twice a month.

Myth 6: You can add all your fish at once once the tank has cycled

When setting up your tank, you must let it cycle first before adding your fish. Cycling a tank refers to the process where beneficial bacteria are allowed to establish themselves in the tank. These bacteria help regulate the nitrogen cycle and help ward off the build-up of ammonia.

When the tank has cycled, you should add no more than two fish at first. The reason for this is that a new tank won’t have enough beneficial bacteria to sustain more fish than that. The first fish that you add will fuel the growth of bacteria till they become fully established.

Depending on your tank size and whether you use any bacterial accelerating products, it will take six to eight weeks to have bacteria fully established. Use a testing strip to check the nitrate, nitrite, and ammonia levels.

Myth 7: You need to change your filter’s media every month

The media that your filter uses is probably a sponge or floss. This medium is where your beneficial bacteria will grow. These beneficial bacteria play an important role in the nitrogen cycle.

Harmful ammonia is created from the waste produced by fish. Beneficial bacteria convert ammonia into nitrites and nitrites to less toxic nitrates. These bacteria don’t live in the water column. Rather, they exist on surfaces, especially filter media.

When you change your filter media, you eliminate many beneficial bacteria. The result is that your water quality may be compromised.

 Regardless of what the manufacturer’s instructions may say, avoid replacing your filter media until it falls apart or is heavily infested with waste and dirt. When cleaning your filter media, only replace half of it at a time. Also, rinse the filter media using tank water to help preserve the bacteria.

Myth 8: Keep one inch of fish per gallon

There is a standard rule that you should keep one to two inches of fish per gallon size of the aquarium. This rule is usually set for those new to fishkeeping, to not overcomplicate things. In reality, what counts is the waste output of the fish when determining how many fish you can place in your tank. The larger the fish, the greater its bio-load.

Another factor to consider is their metabolic rate. Active species will produce more waste than less active ones, given that they are of similar size. You can use the one inch of fish per gallon as a general guideline, but it is also important to consider these other factors.

Additionally, it is important to remember to provide your fish with an adequate amount of oxygen to breathe. A fixed amount of water has a fixed amount of oxygen that it can hold. This is another reason why it’s important to avoid overpopulating your tank.

Myth 9: Bettas and goldfish can survive in a bowl

It’s commonplace in pet shops to see betta fish and goldfish displayed in small bowls. It gives the impression that these fish need minimal care. In truth, these bowls are completely unacceptable for these fish.

These fish need the proper room, filtration, and heating, none of which can be provided by these bowls. A single goldfish should be kept at the minimum in a 10-gallon tank, while the tank size for a betta should be a 5-gallon tank at minimum.

Additionally, these small bowls do not provide a large surface area for proper gas exchange to take place. A square or rectangular aquarium offers a larger surface area to provide adequate surface area for gas exchange.

If you plan to keep two male bettas together, the tank should be at least 30 gallons.  Additionally, each male should keep a ratio of one male per four females. This will help relieve aggression.

Myth 10: Cleaner fish will help keep your tank clean

Catfish don’t eat the waste products of other fish, and plecos don’t eat algae. In fact, they produce more waste than they can remove. As for algae eaters, they’re unable to make a significant difference in the algae growth in your tank.

It’s important to remember that any fish that you add to the tank will produce waste and consume oxygen. Algae eaters and scavengers can help keep your tank clean, but they can’t replace general maintenance.

Beat the myths

Because of all the myths out there about aquarium keeping, I recommend that you do your research and get as many points of view as possible. Though aquarium keeping is becoming more of a science, there is still plenty for us to learn.

Please comment below if you have any questions and feel free to ask about any other myths you might have encountered!

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