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is fish tank water bad for cats

Is Fish Tank Water Bad for Cats?

People who keep fish as pets could also have different animals for pets. I have 2 dogs, Mabel and Dave. Luckily, they don’t pay any attention to our fish tank whatsoever. In fact, I don’t think Dave has even noticed it’s there. He is a puppy though.

This seems to be quite common amongst dogs. They may take an interest and watch the fish moving around the tank, but that’s about as far as it goes.

Cats however, can be a different story altogether!

Some cats develop a bit of an obsession with getting access to the fish tank. This can sometimes cause undue stress to the little guys in the tank.

do cats like fish tanks

Surprisingly though, it’s not the fish they are after, but the water.

It is not advised for cats to drink fish tank water in large amounts, especially if the tank is dirty, as there is a risk of bacteria being spread both from the water to the cat, and possibly from the cat to the water.

It can be dangerous for a cat to drink large amounts of water from your tank if it is a saltwater tank, due to the high amount of sodium in the water.

In this article, I will discuss if it is possible for cats and fish to live together in perfect harmony, and what it is about fish tanks that cats love so much.

Can You Have a Fish Tank with Cats?

It can work perfectly well to keep both tropical fish and cats as pets in your home. Thousands of people around the world manage to do so successfully.

As a pet owner, your primary concern is of the welfare of both sets of animals. Making sure your cat doesn’t stress your fish, and that your cat doesn’t get injured around your tank are both important things to take into consideration.

It is important for your fish tank to be safely out of reach of a cat, and for any electrical wiring on or around floor level to be inaccessible for a cat as well.

Many cats do find fish in a tank fascinating to watch. Some cats have been known to sit for hours watching the fish swim around their tank. Some cat owners have been known to buy fake fish tanks for their cats to watch (I think they are more commonly used as night lights).

Whether you already have a cat and are about to add a fish tank, or the other way around, you will need to keep a close eye at first on how much interest the cat is taking in the fish, and take the necessary steps to keep everyone safe.

The first thing to do is to cat proof your fish tank.

cat proof a fish tank

How to Cat Proof your Fish Tank.

  1. Make sure you fish tank has a lid. Many fish tanks now come with a lid attached on a hinge. They usually have a little feeding hatch as well which you open up when adding food. This is mostly to stop any fishy jumpers making a dash for freedom, but it also comes in very handy to stop any feline paws swiping in the water.
  2. If your tank does not have a lid, make one! It can be something as simple as using mesh netting to cover the top of the tank. The most popular type of homemade tank lid is using plastic or polycarbonate. Best practise is to make sure you drill a few holes into your plastic lid, especially if you have plants in your tank. This will stop too much condensation forming. You could also buy one either online or from your local aquarium if you aren’t a do-it-yourself kind of person.
  3. Make sure all wiring is completely out of reach from inquisitive felines. Whether it be placed securely behind the tank or covered with cable trunking. This is important whether you have any other pets or not. It looks nicer for a start!
  4. Don’t have any furniture right next to the tank that the cat can climb onto to access the tank. This is probably one of the steps that you may need to do if your cat starts taking an interest in the fish tank. If you are unable to move the furniture away, try and place a few obstacles where you can to try and deter the cat from getting to the tank.
  5. Make sure your cat’s food, water and toys are in a different room to the fish. If they are in a separate room, your cat will hopefully spend more time in that room than the one where the tank is.
  6. Get your cat a water fountain. The main reason why your cat is interested in your fish tank is due to the moving water within it. Cats find moving water to be safer than still water in a bowl. Water fountains for cats is an actual thing that people buy, and it works great as a diversionary tactic.

Will Drinking From the Fish Tank Hurt my Cat?

There are a few reasons why your cat would prefer to drink fish tank water rather the water from their water bowl.

Cats are not fond of chlorinated water, so fish tank water being dechlorinated, is perfect for them.

Cats much prefer to drink from moving water rather than stagnant. A tank with an air pump keeping bubbles moving through the water is very appealing to cats.

The water being a little warmer and smelling of fish is also a plus point for any thirsty felines in your house.

If you have a freshwater fish tank which is relatively clean then the only danger really is that of your fish getting stressed or even swiped with a paw.

If your tank is dirty, it won’t stop the cat from drinking the water, but there is a higher risk of an infection due to unsafe water parameters and rotting food.

Saltwater fish tanks are obviously going to contain sodium, which can be harmful for your cat if they ingest excessive or prolonged amounts, as this could lead to kidney or urinary problems.

There is also an element of risk from bacteria being passed from your cat to your fish, especially if your cat is an outdoor cat.

Elements in Fish Tank Water that can be Bad for Cats.

Sodium (saltwater tanks only).

It is common knowledge that too much salt is bad for you. That goes for animals as well.

The following elements mainly apply to dirty fish tanks or brand new tanks that are being cycled and don’t have any fish in yet. If you have a regular maintenance schedule for your tank, and check your water parameters every so often, you are unlikely to have any of the following issues in your tank.


If your tank is new and you haven’t added any fish to it yet, the chances are you are cycling your tank. The first few weeks of the cycle will start off with your tank having very high ammonia levels. This is a normal part of the process until the nitrates, and then the nitrites appear, but, high levels of ammonia in water that your cat then decides to drink from can cause ammonia poisoning.


There is a chance your cat could get nitrate poisoning if he/she drunk from a dirty fish tank regularly for an extended period of time. Ironically, it’s not the nitrates that are poisonous like the name suggests, but the nitrites that they turn into.

Too high or too low a pH level.

Depending on what end of the pH scale your tank water is, if it isn’t hovering around 7, it is going to be either alkaline or acidic.

Rotting food, or even rotting fish!

Rotting food or a rotting fish that hasn’t yet been found or removed will produce high levels of ammonia which is dangerous for cats.

Will Fish Food Hurt my Cat?

are cats ok with fish tanks

Fish Food is generally inoffensive and not dangerous for other animals to eat. If eaten from the top of the tank water by your cat, it will be such a small amount that it isn’t worth worrying about.

For more information about what ingredients are in both tropical fish food and goldfish food, I have written an article about it.

If you leave your fish food next to your tank, ensure you have the lid on it when not in use to stop any curious cats having a little taster session.

What if my Cat Eats my Fish?

fish in the bath

This is actually a very rare occurance.

As I have mentioned earlier, the cats are more interested in drinking the tank water than having fish for lunch.

If a cat is nosing around the top of the tank, the natural instincts of the fish will be to move to the bottom of the tank or to hide away in plants or ornaments. It is their natural survival instinct kicking in.

Cats are not swimmers, and will not volunteer to get into any large body of water.

The only way they have any chance of getting hold of a fish is by swiping it with their paw and flicking it out of the water, or by a fish jumping out of the tank as your cat happens to pass by.

The best way to stop any worry about this is to put a lid on the tank. This will stop any chance of it happening.


Cats are naturally attracted to fish tank water for a variety of reasons, so will want to drink it if at all possible.

If drunk in small amounts, it is unlikely to harm your cat, but it could stress your fish out.

Cover your tank and make it cat proof.

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