Common Mistakes

It’s easy to make aquarium mistakes when you’re a beginner. Fortunately, you can avoid them. Read on and learn how to set your new aquarium up for success!


1. Overfeeding the fish. Because fish feed often comes with instructions to feed the fish 2-3x a day, new aquarium owners almost always fall to this habit. Resist the urge to feed your fish several times a day. Feeding produces waste, and waste produces ammonia, which produces nitrites. Both are toxic for your fish. If more ammonia and nitrites than your aquarium’s beneficial bacteria can handle, your fish die.

Feeding Fish
Fish Scrambling for Food

So feed your fish no more than once per day. Fish can go on without food for days, so don’t worry about not feeding them even if they look hungry. Additionally, if your ammonium and nitrite levels are high, completely forego feeding them for at least two days. Also, please don’t feed your fish the first day you put them in your newly set-up aquarium. It’s always wise to give the environment time to balance itself.

2. Adding the fish too soon. New, over-eager aquarium hobbyists often add fish immediately to their newly set-up aquarium. Don’t. Newly set-up aquariums aren’t stabilized yet, meaning they are full of harmful chemicals to your fish. Wait at least three days before adding your fish.

3. Putting the fish all at once. One of the most common aquarium mistakes new hobbyists make is putting their fish in the fish tank all at once. The nitrogen cycle occurs slowly, so you should also be slow in adding fish that produces harmful waste products. Add 3-5 fish only in your tank, three more after a week interval, until you reach the ideal number of fish for the size of your tank.

4. Overstocking. Putting too many fish in the tank is another common mistake. The general rule of thumb is one adult fish per gallon for freshwater fish and one adult fish per 2 gallons for saltwater fish. Keep in mind, though, that your aquarium decors and equipment also take space. So, consider going below the one fish:1 gallon /1fish:2 gallons ratio, and there should be enough water space for your fish to move.

5. General ignorance of the Nitrogen cycle. Most new aquarium hobbyists are simply not aware of the importance of this cycle. Realize that a fish tank is enclosed and therefore contains all the natural waste of a fish, producing ammonia. If the water is not safe for the fish, you’re not recreating their natural environment. Fish tanks need to undergo a complete nitrogen cycle. This way, you can be sure that the beneficial bacteria present are adequate to kill harmful bacteria.

6. Starting small. New aquarium hobbyists are often under the false notion that it’s easier to start with a small fish tank. This is wrong. Smaller aquariums are much difficult to maintain, but bigger aquariums give you enough room to make aquarium mistakes. The toxicity level of your water always goes down when there is more water. So get a giant aquarium. Ideally not smaller than a 20-gallon. But the bigger, the better.

Small Aquarium
Goldfish in small Aquarium

7. Putting together aggressive and peaceful types of fish. Another one of those aquarium mistakes that new hobbyists make is putting aggressive fish together with peace-loving fish. If you want aggressive fish, stick with aggressive fish, but otherwise, aim for a harmonious co-existence. Pick peaceful types of fish and fish that get along well with each other. The sales assistant of your local fish store should be able to help you with this.

8. No regular water testing schedule. While some aquarium owners don’t spend enough time performing water tests, some new ones aren’t aware that one should perform water tests. The overall health of your fish depends on the quality of water. So, test for nitrite and ammonia levels in your water at least once a month. You want a zero for both ammonia and nitrite.

9. No regular water change schedule. Water should be changed at least once a week. This will ensure that nitrates and nitrites are eliminated regularly. A healthy aquarium environment starts with manageable nitrate and zero nitrites. You can achieve that if you perform water changes regularly.

10. Using the wrong filter size. Because new aquarium owners tend to know little about aquarium equipment, they often buy the wrong ones. Know that the size of your filter should be adequate for the size of your tank. Your filter should do its job at least three times in an hour. If it doesn’t, your filter is too small, and you’re putting the life of your fish at risk.

Filters remove excess food, fish waste, and other decaying microorganisms. Remember that they all contribute to the ammonia and nitrite levels of the water. That said, it’s OK to over-filter and get a larger filter than to under-filter and buy a smaller, inadequate one.


Beginner Aquarists are usually very eager to get things going. Yeah, it is exciting to start a new journey- let alone embarking on a fishkeeping journey!

However, this excitement often causes heaps of trouble. You have to control yourself. Even though your intentions may be good, if you don’t follow the manual, you will end up with stressed or dead fish.

Do not fret. Every expert started where you are now. In time, you will know your way around the world of fishkeeping. Until then, try and avoid making the above-mentioned mistakes!