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Common Mistakes

20. Not enough hiding spots

Many territorial fish require hiding places and some non-territorial fish appreciate them as well. They need safe places to feel secure and to hide in when they are being picked on or when they rest. Not having an adequate number of hiding spots in your aquarium can stress your fish, ultimately leaving them more prone to disease.

19. Misdiagnosing

You think you see a small black speck on one of your fish. Quickly, you run to the store, return with medicine, and dump it into the aquarium. The next day, fish start swimming upside-down and you go buy more medicine. Over the next few months, you dump more and more medicine into the tank and your fish get sicker and sicker. All of this could have been avoided if you had taken the time to correctly diagnose the problem in the first place.

18. 100% water changes and removing fish for water change

100% water changes are bad for your fish in multiple ways. First, they require you to take the fish out of the water. This could potentially rupture its swim bladder and/or scrape off the essential slime coat. Second, people who perform 100% water changes often rinse their gravel with tap water as well, thinking that squeaky-clean substrate is preferable. This action actually removes the beneficial bacteria that keep your tank cycled. Finally, this causes a sudden change in water parameters. In order to safely put the fish back in the aquarium, you would need to extra time acclimating them. To safely put the fish back in the aquarium, you would need to spend about an hour acclimating them.

17. No quarantine tank

You buy some new fish from your local fish store and place them directly into your tank along with your other fish. The very next day, your old fish have white spots and blackened fins. They sit on the ground, fins clamped, only moving to rub against tank walls. Quarantine tanks are used to isolate new additions to your tank before adding them. The quarantine period will allow you to identify and treat any pathogens that you do not want in your main tank.

16. Using too many chemicals

If fish get sick, you put chemicals in the water. If the pH is off, you put chemicals in the water. When you start a new tank, you put chemicals in the water. Don't get me wrong—using chemicals can help fish. Your fish would die if you didn't dechlorinate their water. However, chemicals should be used in moderation. Some chemicals adversely affect fish and using them unnecessarily is not recommendable.

15. Starting with a small aquarium

Small aquariums are more prone to temperature and parameter changes. These are both very stressful to fish. Small aquariums also can't host many different kinds of fish, allowing less mental stimulation for the inhabitants. Aquariums over 10 gallons are much better for the fish.

14. Not acclimating new fish

In the wild, fish have relatively stable temperatures and water parameters. In an aquarium, you have to keep these stable to keep the fish happy. When fish switch aquariums [or water], they need to be slowly acclimated to the new water (this can take around an hour, possibly longer for certain, more sensitive species).

13. Thinking that something will work out for you because it did for someone else

”Bob kept his goldfish in a bowl and it lived for 6 months. That's a long time, so maybe I should do the same thing.“ First of all, goldfish can live for 40 years. Your average goldfish also needs at least 25-30 gallons. Believing others unwaveringly can have consequences for your fish. Always check with multiple sources before taking action.

12. Overfeeding

Many people say to offer what fish will consume in a few minutes, but this is not true. I feed a sinking algae wafer to my 29-gallon community tank and it takes a few hours to consume. I also feed them Hikari Micro Pellets and they finish those in about 15 seconds. It is best to start low and get a feel for how much they need.

11. Stocking the aquarium too fast

Fish produce ammonia. Via the nitrogen cycle, this highly toxic substance is converted into nitrate, a much less toxic substance. For the nitrogen cycle to work, it requires some beneficial bacteria. If there is an overload of fish (ammonia) at once, there will not be enough bacteria to keep of with the fish waste. Add a few new fish at least a week apart.

10. Not testing water parameters

Imagine this: Your tank turns slightly cloudy. You wonder what is going on but do nothing. The next day, all of your fish are dead. This was probably a nutrient spike. If you had tested water parameters, your fish could have survived. Liquid test kits are better than strips because they are more accurate.

9. Trusting the LFS (local fish store) and no one else

See number thirteen—this is a very similar mistake. Many LFS employees are knowledgeable, but not all are. As mentioned in #13, always check facts with multiple sources.

8. Over-cleaning

Over-cleaning is bad for fish because it can stress them and because it removes beneficial bacteria. Now, this is not an excuse to skip out on water changes. Just don't replace filter media all of the time or replace some of it at a time. Also, don't do 100% water changes unless you really need to. Finally, make sure not to clean using harsh chemicals unless nuking a tank.

7. Unawareness of the nitrogen cycle

The nitrogen cycle is the period in which beneficial bacteria establish to remove the toxic compounds from decaying organic matter. The aquarium requires extra maintenance during this period. You can read more about it here.

6. Overstocking

Overstocking is detrimental to fish health. It causes stress and the build-up of fish waste, overall resulting in bad conditions. However, tanks can be successfully overstocked if you constantly maintain them and provide hiding spots.

5. Lack of maintenance

How hard is it to do a water change or feed? Many people decide to skip out on these important things because they feel that they don't have time. You could just drop some food in (10 seconds) and drain some water out with a siphon and replace it (15 minutes). If you don't have time for maintenance, you probably shouldn't have gotten fish in the first place. However, if you really care about the fish, you will be able to find at least some time to care for them.

4. Not dechlorinating

Apart from getting fish right away and impulse buying, this is probably the most common newbie mistake. To remove bacteria and other bad things from water, virtually all water that comes into your house is treated with either chlorines or chloramines. Both are extremely toxic to fish. Without removing, detoxifying, or binding these chemicals, most fish will not make it past 24 hours. Some hardy fish (including goldfish) may be able to survive low concentrations for awhile, but it will most certainly still be detrimental to their health. To remove chlorines and chloramines, I recommend a high-quality, concentrated dechlorinator such as Seachem Prime.

3. Inadequate filtration

I have a friend with a mid-sized tank and one HOB filter that looks pitifully small for it. If you buy a kit, the filter that comes with it isn't usually powerful enough. A good rule is to make your filtration 2x as powerful as recommended on the box. If it says 'for 10-gallon aquariums,' buy two, or upgrade to a larger version.

2. Incompatible fish

Before acquiring any new fish, make sure to research a lot. I can't stress this enough. You can't even fathom how many people end up with cichlids and goldfish, angelfish and small shrimp, or multiple male bettas in the same tank. These and many other stocks are definitely incompatible. You mainly have to worry about parameters, temperatures, and decorations/plants/substrates. However, some fish don't get along very well, despite having the same requirements. For example, the betta (esp. male) or Endler's Livebearers and Lyretail Guppies. Make sure to research and ask questions first.

1. Impulse-buying

How many of you have come home with a new fish just because it "looked cool"? Before acquiring any new fishy friends, or even a new plant, make sure to do lots of research. This will save you much stress and money. Many people end up with a goldfish in a bowl or a red-tailed shark and a common pleco in a 10-gallon aquarium. These are both completely unacceptable and could be avoided with some prior research. They would have to either return the fish (which they may have been emotionally attached to) or buying a large tank.


Thank you for reading this article on common mistakes (published in 8th grade—10/26/14, last edited 4/18/17)! For more information, please browse around AquariumKids.com. Feel free to contact me at evanb [at] aquariumkids [dot] com with any questions :)