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Can a Rainbow Shark Live in a 20 Gallon Tank?

So, Can A Rainbow Shark Live In a 20 Gallon Tank?

The short answer is No, a 20 gallon tank is actually not the most suitable living place for a rainbow shark. We may sometimes consider a 20 gallon tank to be a good size for most fish but in the case of the rainbow shark, the fish will actually get too big for its tank at some point.

You will most certainly have to make sure you go for something bigger from the very start of your venture with adopting a rainbow shark. 

Rainbow sharks are actually quite small but the tricky part is that most people do not know in advance how big a fish can get, therefore making the mistake of putting certain fish in a smaller tank. One of those cases is most certainly the one for rainbow shark.

What are Rainbow Sharks also known as?

Known also as Red Fin Sharks or even Ruby sharks, the rainbow shark is one of the many small tropical freshwater fish that are native to Thailand. 

As you may have guessed already, they are known for their vibrant red fins but something also makes the Rainbow Shark stand apart from the rest of the other fish in the waters of Thailand, is the fact that it likes to act in a very territorial manner. 

As a home-pet, the rainbow shark is a quite difficult one and it requires all sorts of unique attention in order to keep it healthy and happy too in its newfound environment.

Deciding the size of the tank you need, what other fish you can put in the aquarium and how you should decorate your aquarium are all just a few of many questions that you should be asking yourself when acquiring pretty much any type of fish to put in an aquarium.

So, join us as we explore all sorts of questions, such as, where should we be placing the fish’s tank, and so much more...

What is the best size tank for a rainbow shark?

The minimum size of tank you should be looking at in the case of the rainbow shark is around 50 gallons. Should you have the choice of going a bit higher, depending on space availability and financial ease, then you should definitely opt for that option instead.

The bigger the tank is, the happier and free the fish will feel. It is generally not expected of fish in captivity to act their normal, just as they would in the wild and that is for numerous reasons.

One of them being the size of a tank and the feeling that we as pet owners give them through the size of the tank that we choose for them. As an example, an ideal tank for multiple rainbow fish would be a six foot long, 125 gallon tank.

Things start to become much more difficult though once you decide that you want to have more than one species of fish in the tank.

Rainbow sharks are generally hard to keep without any issues in an aquarium environment with other species due to their very intense territorial behavior. One of the things that play a major role in suppressing that behavior is most definitely the size of the tank.

If you are expecting to have quite a few fish swimming in your aquarium, you should invest in a much bigger tank in order to make sure that that the rainbow shark does not just bully everything else in the confined space it is living in.

Where Is The Best Location For The Tank?

Just like most other fish, some place in the house where the lighting is at a medium level is the most perfect place for your rainbow shark tank. There are various types of ways in order to achieve medium light of course and most of those are artificial.

Through the use of various types of aquarium lighting, such as T8 and T5 florescent bulbs, you can adjust your aquarium’s lighting according to the needs of your fish, ​aquariumGardens tells us.

In the case of rainbow sharks, knowing there will be plenty of vegetation in the aquarium as well, LED lighting can also be considered for a much better visual effect on the aquarium. 

First and most importantly though, before going all out with LED lights, you should care for finding a solution to keep the lighting at the right level.

What Decorations Should You Put On The Bottom Of The Tank?

The territorial behaviour of rainbow sharks is something that is extremely important in this case. Rainbow sharks need a lot of hiding spots since they love hiding.

These can come in the form of caves, rocks or some types of carved woods. On top of that, some dense vegetation as well as some other plants could be placed in the tank in order to prevent algae and keep the fish distracted.

The bottom part of your tank should have sand as it is what this type of fish is most used to in Thailand. Last but not least, make sure you have closed your aquarium well because rainbow sharks are actually quite good jumpers and you do not want to have any jump-out-of-aquarium incidents while you are away.

How Should You Treat The Water?

There are certain things that need to be taken care of regarding the tank and the condition of the water before you throw your rainbow shark into your tank’s water. Amongst those things is changing the water to have a pH level at 6.5-7.5 and the water must have a hardness of 5 to 11 DH, according to ​fishKeepingWorld.

The pH level must generally remain more or less stable at all times since changes in the level can sometimes cause a rainbow shark to become more aggressive than usual.

When it comes to water treatment, it is quite important that we follow the guidelines given to us by experts on these matters, otherwise we end up endangering the lives of our pet fish.

On top of that, it is good to know little details about the chemicals we handle on daily basis, lest we accidentally introduce them into the tank and alter the recommended pH balance.

What Is The Best Temperature For The Tank?

The water of the tank must have a temperature of 75 degrees F to 81 degrees F. This is quite important as the rainbow shark is a small fish and sudden changes in temperature can result in the fish changing its behaviour very drastically.

Not only does the behavior of most fish change when there is an abnormal change in temperature but when we have quite a few different fish in a tank, it may all result in a big mess. This is because the fish will become quite disoriented and start acting aggressively against each other.

What Is The Best Food For The Rainbow Shark?

Rainbow fish mostly consume algae, some insect larvae, decaying plants they find in their environment and sometimes chunks of meat such as zooplankton.

They are generally known to be quite easy to feed since they eat a little bit of everything. It is generally suggested that their diet is kept as diverse as possible so feel free to buy all of the already mentioned types of food they consume to give to them.

If you would like to have their colors remain as vibrant as possible though, meat (fresh or frozen) is what you should be feeding them the most, according to ​fishKeepingWorld

This is even more important for younger rainbow sharks as they tend to grow with very healthy and vibrant colors when they have spent most of their youth consuming various types of meat.

How Often Should You Clean The Tank?

In most cases, this depends on how many fish you have living in the aquarium, how big the aquarium is and in some cases, the types of fish that you have living in there.

The average and suggested frequency for cleaning an aquarium is once every two weeks or so and should involve all standard suggested procedures in order to make sure that the aquarium is indeed clean enough to provide a healthy living environment for your pet fish.

According to ​kingBritish, the procedures are basically:

  • Changing about 10 to 15% of the water in order to have it clean up a bit and removing any leftover foods with gravel from the bottom of the tank.
  • Wiping the glass of the tank really well in order to remove any leftover algae.
  • Checking the filter to see that it is operating well and is clean enough to be kept in place. Most filters have instructions on how they should be cleaned and in most cases you would have to just clean up the sponge that is inside your aquarium’s filter.

In the case of the rainbow shark, the aquarium should be cleaned a little bit more frequently than normal, since you will most probably be pouring algae as food for your pet fish, therefore making it much easier for your aquarium to become smelly.

On top of that, testing your water’s quality regularly should be something you get used to because most fish can become quite disoriented and behave weirdly if the water’s quality deteriorates in any substantial way.

What Are The Best Tank Mates For Them?

As we have already explained, the rainbow shark is not exactly the most “quiet” type of fish and due to its territorial behavior, you might not want to have other types of fish (or even other rainbow sharks for that matter) in your aquarium living with your beloved rainbow shark, especially not types like the red tail catfish.

Most other types of fish are quite shy and will end up having issues with a rainbow shark due to its intense behavior. That is mostly due to the enclosed nature of the aquarium, making the rainbow shark want to assert dominance in its environment.

Should you actually decide to try having more than one species in your aquarium, then you should try to have types of fish that do not lurk at the bottom of the aquarium as this is where rainbow sharks usually go.

Other than their bottom-dwelling nature, rainbow sharks also tend to mostly dislike fish that look like them or are of somewhat the same size. For that reason, you should be avoiding catfish or red tail sharks for example because those are just bound to bring up issues in your aquarium life.

If you really want to have more than just a rainbow shark though, another tip would be to find fish that can actually defend themselves, such as Gouramis and Barbs. Also, make sure you the rainbow shark is the last fish you add to your aquarium, otherwise it will make territorial claims much faster and cause way more problems than it should.

Is It Easy To Breed The Rainbow Sharks?

Rainbow sharks tend to mate around the October – November period when left in the wild and that is also the time when this type of fish reaches its sexual maturity.

This all depends heavily though on various things, such as changing seasons, local temperature and the length of a normal day in those months. Breeding is done in a very similar manner to other known fish breeding procedures and that is by having the female lay down eggs and then the male passing over them to fertilize them. It takes no more than a week for the eggs to hatch.

We are sorry to say though, that there haven’t been very many good stories on rainbow shark breeding inside an aquarium, so in the case of rainbow sharks, we would suggest you avoid any efforts of doing so.

The main reason for the unsuccessful breeding of rainbow sharks is their territorial behavior and since the aquarium is a very confined living space for most types of fish, the rainbow shark cannot breed naturally very effectively in there.


We hope that you found this article as you expected it to be. Rainbow sharks can be a tricky type of fish to have as a pet but we have gathered enough information on how to cater for one that it shouldn’t prove too difficult to do so, as long as you follow the instructions given to you.

So, what is your take on rainbow sharks? Would you have one in your aquarium, despite them being a quite feisty species of fish? Do you think it is too much hassle? Or do you think they are actually too pretty of a fish to have floating in your aquarium to pass on? Tell us in the comments below!


Hey, thanks for passing by, welcome to the blog for Pet Fish fans. This is me, Wayne, and my son Theo. I started this journey after we bought him hist first Fish Tank of fish. Follow my site for my research and info on Pet Fish.