15 Things Not to Put in a Fish Tank for Safety of Your Pet Fish

Things to Avoid in an Aquarium
By Garrison Hickles Updated

Like you in your home, fish and aquatic species also need a clean and secure house to live in. So, while decorating an aquarium or living place of your little aquatic friends, try to make it safe and hygienic like your own home. It’s quite obvious that you love your cute swimming-companions like your children, so why should you compromise their safety and comfort by putting unnecessary things in the tank? Always try to keep an aquarium germs-free by not putting any toxic chemicals, bacterial substances, and hazardous products.

Things to Avoid in an Aquarium

You may want to decorate your fish tank with different new materials, but that doesn’t permit you to compromise the hygiene and health of your little pet fish. A little cautiousness of yours can save the life of your little aquatic friends. Take a detailed look at a few things not to put in a fish tank:



You will get many plastic toys, show pieces and painted objects in the market to decorate or rejoice your finned-buddies, but do you know whether those things are safe for the fish tank or not? Don’t experiment with the life of the innocent aquatic animals by choosing the wrong decorations. This may embellish the looks of the fish home but may also be the reason for their unexpected death.

Plastic objects release chemicals and toxins in the small aquatic family of the cute fish and result in choking hazards which can be the primary reason for multiple illnesses and infections. The toxic chemicals add poison to the water of the tank, and if the fish chew or lick the plastics then that compounds may be the reason for their death. So, try to be cautious before choosing any decoration for an aquarium.


The paints on the plastic objects are poisonous and can kill your pet fish if it licks the paint.


Untreated Wood

Yes, you can put driftwood or finely shaped wooden decorations in a fish tank because some fish really like consuming the algae on the driftwood. Moreover, finely designed wooden decors can bring a great look to your aquarium. However, expert aquarists give an important caution to never put un-treated woods, hardwoods, and decomposed woods in an aquarium.

Keeping hard and crude wood may hurt your little buddy when it tries to swim and play in the water. Also, putting the decayed or decomposed woods may tend to spread poisonous infections and hazardous diseases. Thus, avoid using unshaped woods as the hiding place or décor for the fish tank.



Ceramics to be Avoided for Keeping in a Fish Tank

Many people often keep ceramic in their fish tanks because it is used whether as a decoration or as a hiding place for the little fish. Now, it’s really okay to keep hiding places in the fish tank, but use caves or small wooden houses rather than ceramics in the aquarium.

Ceramics are the polished clay potteries made of terra-cotta clay and lead which are harmful to the aquatic species. If your little buddy tries to lick and chew the ceramics then it will really result in dangerous diseases, poisoning, color-fading, wings-loosing or death of the fish. Therefore, remember taking care of your pet fish is your first priority rather than providing them a hiding place or adding an adornment at the fish tank.


Sharp Objects

Just like human beings, fish and other aquatic species in your aquarium should not be kept in contact with sharp objects which can injure and harm them. The sharp-edged objects like rocks, spikey decorations, sharp gravel, painted glass, etc. may result in cuts and bloodsheds, which can be the reason for the suffering and death of your innocent pet fish.

So, always be very careful in choosing the home ornaments of the fish breeds. Whether the species is small or large in size, you must avoid putting any kind of sharp things in the bottom part of the fish tank that can hurt the species accidentally.



You may have seen water fountains and large size tanks in aquatic museums where people throw coins to wish luck for themselves. But never try to do this mistake when you are keeping an aquarium in your home. Remember, the fountains and big aquatic museums are large in size and they are cleaned every day by the workers who maintain the places. However, you cannot clean your fish tank regularly. Moreover, stop having the misconception that your pet fish are successful in fulfilling your wishes.

Coins are made of copper which is dangerous for every living being including fish. Copper releases bad toxins and injurious chemicals that are sources of making the water of the fish tank poisonous and life-threatening. Fish and other aquatic species can never live in such a poisonous environment, and to save them from dying, never keep a single coin or other metals in your fish tank.



You may want to light up your fish tank to bring gleaming effect, but put the light on the top-most part of the ceiling. Never keep the light in the bottom part of the water, and also don’t keep other electronics like battery and sound device in an aquarium. These are the hazardous things that are suggested not to put in a fish tank for the safety of the pet fish.

Keeping unnecessary electronics may result in an electric shock, and also the rust-particles of the batteries or other electronics are poisonous which can be life-threatening for your little pet fish. It is really not necessary to add sound effects or light effect in your aquarium because the security of the pet aquatic species is much necessary and because of fixing electronics in the tank the fish may get accidental death due to short circuits. Just light up the fish tank by fixing the light on the upper portion of the aquarium.


Beach Sand

Avoid keeping beach sand in both freshwater and marine water aquarium because sand is generally polluted with germs, dust and chemical residue, which can harm your tiny buddies in the water. Don’t compare natural sand in the wild with the ambiance of your aquarium because when a fish is living free in a sea, it gets a huge space, but the story is not same for the fish tank.

So, avoid pollution and germs by not keeping beach sand as a décor to your aquarium. There are other options to decorate your fish tank in a simple way.


Chemical Solutions

Always try to clean your aquarium with a mild or soft liquid that has very less chemicals. The smell of the harsh chemicals disturbs the fish breeds and causes harmful skin diseases also. Moreover, some people add chlorine or other chemical substances in the water to clean the dirty water in the fish tank but it’s really not a good idea. If possible then try to change the water 3-4 times in a week to maintain the hygiene but never add any kind of chemical toxic solutions to the water.

Remember, this short-cut option of cleaning the water by adding preservatives and chemicals will harm the innocent aquatic creatures by causing several diseases or dangerous death. So, don’t be an unnecessary reason for the demise of your little friends by choosing the wrong idea of cleaning the aquarium.


Untreated Rocks and Gravels

You can definitely keep fine gravels and shaped rocks in an aquarium but never keep any untreated sharp rocks and hard gravels at the bottom part of the fish tank. Don’t throw rocks from outside that can injure the fish with cuts.

Moreover, the unshaped rocks or gravels may have edged corners that can harm fish, which will obviously harm the fish with fungal and bacterial infections.

If you want to keep the rocks at the bottom of the aquarium clean then wash them and shape them by removing the sharp edges. Make sure that the rocks and gravels should not harm the water species in anyway.


Thorny Plants

Thorny Trees Which Should Not be Put in a Fish Tank

Avoid keeping thorny plants and herbs in an aquarium that can prick or hurt the fish and other aquatic species in your fish tank who don’t know how to be careful. It’s only your responsibility to safeguard them from the thorny and bushy things that can injure them internally or externally with bleeding.


Things that Looks Like Fish Foods

The cute little fish have less idea in identifying their food, and also have a bad habit of biting and chewing different things in the tank. Therefore, don’t put any unnecessary soft chewable toys, human foods like bread or chips because these are not good for fish.

Soft toys release chemical toxins that can be life-risky for the fish, and chips or bread are human foods which cannot be digested by fish, as they have a different digestive system. Moreover, chips have salt which is not good for the appetite and living conditions of the freshwater fish. So, think twice before putting harmful and unnecessary objects in a fish tank which can be hazardous for your pet aquatic species.


Things that May Get Decomposed

Avoid putting worms, dead bugs and snails from outside to your fish tank, because you need to check the hygiene and health requirement of the pet-fish like your children. Feeding dirty and dead animals to the fish breeds may adversely affect their immune system. Moreover, they have the habit of eating live worms, so go to a pet food store and either purchase live blood worms or frozen foods for fish that are safer and healthier than the foods in wild.

Adding the dead shrimps, worms, and snails in a fish tank will also decompose and make the water polluted. Consuming the wasteful dirty water or living in the decomposed or degraded ambiance may be the reasons for multiple fungal and bacterial diseases which can result in the death of the fish. Sometimes, a poor environment is the reason for stress and anxiety for the fish.


Wrong Fish Breeds

You have to select suitable companions for every fish in your aquarium, because putting the wrong species may cause fighting and other problems between the fish. Never keep aggressive fish with peaceful breeds because that can result in fights and bloodsheds.

Also, never keep large fish breeds with the small one because the big fish often eat the small species. Therefore, try to keep the same types of species of a similar size in a fish tank. Moreover, get proper knowledge about the compatibility of every fish and then keep the breeds together.


Corals and Oysters

Corals Which Should Not be Put in a Fish Tank

If you are planning to make a marine aquarium then shells, oysters, corals and other living fruits of the sea are perfect to create reef ambiance in the aquarium. But, while keeping freshwater fish in an aerated fish tank never put any sea creatures, sea plants and marine ecosystem related things in the aquarium.

Find another way to decorate your freshwater fish tank other than keeping seawater animals, plants or other objects in a freshwater aquarium because corals and shells have pH, hardness and high chemicals that can determinate the health of the fish of freshwater. Also, the sharp-edged of reef objects may cause injury to the unhabituated fish brought from deep rivers. So, don’t make their ambiance uncomfortable with wrong decoration.



You can put your hands to feed your fish sometimes but clean them with mild liquid hand soap, creams and sanitizer before putting your hands in the water of the fish tank for feeding the fish, taking out the eggs of the fish or shifting one fish to another place. Putting dirty hands in the water may result in the downfall of the healthy fish in the tank and spread infections.

After washing the hands, rinse them with a clean towel and put them in the tank because of the chemical residue of the soap is left in your hand then it may result in a choking problem and it may spread toxins in the water.

Considering all these aforesaid suggestions may help you keep your pet species in the aquarium happy and healthy. It will also help you have a clear knowledge about the things not to put in a fish tank that can harm the innocent and tiny aquatic creatures.


  • Use tested and authorized decorations for your aquarium that are guaranteed to be safe from the market.
  • Never allow the dead or decomposed fish corpse to stay in the aquarium that can spread infections.
  • Try to keep the fish tank spacious by not overcrowding it with different fish of separate communities.
  • Buy fish foods from good stores then only put them in the tank.
  • Take suggestions from fish pet stores who can tell you about the correct decoration of the fish tank.

Know about More Fishkeeping Ways and Better Cleanliness of the Fish Tank

You may also acquire information on other tips, care guides and suggestions to keep your pet fish safe by having a look at a few topics: