How Big Do Comet Goldfish Get: Tank Requirements | Aquascape Addiction

How Big Do Comet Goldfish Get: Tank Requirements

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A detailed guide on how big comets get and the ideal tank and care requirements for them, many people seems to get this part wrong, don't make the same mistakes.

How Big Do Comet Goldfish Get: Tank Requirements

If you have never heard of these fish before, Comet Goldfish have become increasingly popular across the world. This is a specific type of goldfish, one of many, and many claim it’s one of the coolest ones.

Today we want to provide you with all the basic info you need about these fish. So, how big do Comet Goldfish get? Well, your average Comet Goldfish is going to max out about 12 inches in length.

Let’s talk about comet fish size, tank size and requirements, how to make them grow fast, and so much more.

Comet Goldfish – The Origins

orange comet

Let’s provide you with a little background info about this neat looking fish, which is because the Comet Goldfish did not actually exist until a couple hundred years ago.

This is a type of fish that was made in the USA by a man named Hugo Mullert. The Comet Goldfish is a fish that was created in captivity by breeding the common goldfish a certain way.

Common Goldfish with distinct characteristics were bred with each other, along with other types of goldfish, to produce the Comet Goldfish. Now, this is the first goldfish of its kind, the first type of single tail goldfish out there.

The Comet Goldfish and the Common Goldfish are close relatives, which is why the are often confused with each other, but rest assured that they are certainly not the same fish.

So, How Big Do Comet Goldfish Get?

Your average Comet Goldfish is going to grow to around 10 inches in length. That being said, these fish can grow anywhere from 8 to 12 inches in length.

They usually top out at 12 inches or 1 foot in length. For the most part, within an average sized aquarium, they will top out at 8 inches, but can indeed grow to a full foot in length when kept in ponds.

How Fast Do Comet Goldfish Grow?

Comet Goldfish do of course start out as small fish fry. During the first few weeks of growth, you can expect them to grow by about 50% of their size each week. This rate of growth then slows down significantly after the first few weeks.

The growth rate of a comet goldfish, once those first few weeks are up, will be a small fraction of an inch per month.

You can expect a Comet Goldfish to reach its full size within 3 to 4 years of being born.

That being said, just like most other types of goldfish, the Comet Goldfish will reach sexual maturity within 12 to 14 months of being born, or in other words, this is when they will be ready to reproduce.

Types of Comet Goldfish

silver comet goldfish

Many people do wonder what the different types of Comet Goldfish are, or if there are in fact different types of Comet Goldfish.

Comet Goldfish can come in a few colors including red and white (Sarasa), white, brown, yellow, and black (Comet & Koi Hybrid).

There are a couple of other types of Comet Goldfish, although they are fairly rare.

The Sarasa Comet

One such variation is known as the Sarasa Comet Goldfish, which has a red and white color scheme with long and flowing fins. Sarasa Comet Goldfish look very similar to Koi.

The Tancho Single Tail

The other main variety of Comet Goldfish is the Tancho Single Tail Comet Goldfish, which has more or less the same body as the normal Comet Goldfish, but is silver in color with a red patch on its head.

How Can I Make My Comet Goldfish Grow Faster?

The fact of the matter is that you may not want to wait for a full 4 years for your Comet Goldfish to reach its full size.

Now, there are in fact some things which you can do in order to slightly speed up their growth rate, not by a whole lot, but every little bit counts. So, how can you make your Comet Goldfish grow faster?

The Right Food

One of the things you should do if you expect your Comet Goldfish to have a fast growth rate is to feed it the right food.

The most important factors here are that the food is very rich in protein and high alkaline. In other words, high protein food specifically designed for Goldfish is what is recommended here.

A Large Tank

We will touch on the ideal tank size for Goldfish below, but it is important to note that Goldfish and many other fish do grow somewhat according to their environment, specifically the size of their habitat.

Simply put, Comet Goldfish that live in larger tanks tend to grow larger than those living in smaller tanks.

This is why Comet Goldfish living in ponds often grow to a foot or longer, whereas those living in aquariums tend to top out at around 8 inches.

The Right Water Conditions

This is another aspect we will touch on in greater detail below. However, the fact here is that super clean water is going to help a lot.

You want to have a great filtration system that can remove as many unwanted contaminants as humanly possible.

On that same note, water temperature, the pH level, and the level of general hardness will all make a difference here as well. Side note, Goldfish are always hungry and they love to nibble on algae for sustenance.

In terms of Comet Goldfish growth rates, having a bit of algae in the tank can in fact be beneficial in this regard.

Comet Goldfish Tank Size

Ok, so above we talked about how you can make a Comet Goldfish grow faster by ensuring that they have a large and spacious tank.

How Many Gallons Does A Comet Goldfish Need?

Well, what qualifies as a good size tank for Comet Goldfish? The recommendation for Comet Goldfish is that each fish requires a 50 gallon tank at the least.

Now, do keep in mind that this is the absolute minimal tank size. We personally would recommend that a Comet Goldfish be kept in a tank of 60 or even 75 gallons, especially if you want it to grow faster and bigger. Speaking of 1 Comet Goldfish, what about 2 of them?

Well, these fish do love their space, so if you plan on keeping more than 1 of them together, it’s a good idea to ensure that each fish has around 75 gallons of tank space to work with.

Therefore, if you want to have 2 Comet Goldfish, a tank of 150 gallons in size is recommended.

Comet Goldfish Tank Conditions & Parameters

We did touch on this above, how the right tank conditions and water parameters can make a difference in terms of size and growth rate.

Not only that, but of course, the right tank conditions and water parameters will also ensure a happy and healthy goldfish.

Let’s take a look at what your tank should feature and what the water needs to be like in order to provide your Comet Goldfish with the best possible environment, so they can grow as big as can be.


Comet Goldfish produce an astounding amount of waste, and you therefore need a high powered filtration unit that can live up to the task. A rule of thumb is that a good aquarium filter should be able to process at least three times the amount of water in a tank every hour (we have reviewed our top 6 filter picks here).

Therefore, for a 50 gallon Comet Goldfish tank, your filter should be able to move at least 150 gallons of water per hour.

Also, keep in mind that you do want your filter to feature all 3 major forms of filtration, these being mechanical, biological, and chemical. Also, a 30% weekly water change will go a long way in maintaining a clean tank, and therefore good health.

Water Parameters – Temperature, pH, & Hardness

The water temperature for Comet Goldfish should be between 50 and 75 degrees Fahrenheit, with around 60 degrees Fahrenheit being the ideal.

Therefore, since these fish do fine in cooler water, chances are pretty big that you won’t need any kind of heater to keep them happy and healthy.

In terms of the pH level, the acidity should be kept between 6.5 and 7.5. A perfectly neutral pH level of 7.0 on the dot is best. The water hardness for Comet Goldfish should be between 5 and 19 dGH.

Lighting, Plants, & More

For Comet Goldfish, some basic smooth gravel substrate is fine. You do want to provide these fish with a fairly heavily planted tank to keep them happy and healthy (more on substrates on this article).

Remember that live aquarium plants produce oxygen and they help filter the water too (here are some safe picks).

If you are worried about oxygenation, you can also get an air pump and/or air stone, although it is not necessary. Finally, a moderate amount of lighting will do fine.

Comet Goldfish – Feeding

As touched on above, high quality Goldfish food that is very rich in protein is recommended for Comet Goldfish.

These fish are omnivores, so they should be eating pure protein, and yes, they do like some boiled veggies, aquarium plants, algae, and other plant matter.

A well balanced diet that is high in protein is what you need to go for if you want your Comet Goldfish to grow as big as can be.

Besides regular fish food, some of the best foods for Comet Goldfish include small insects and insect larvae, blood worms, worms, and other such protein rich critters.

For veggies and greens with lots of vitamins, foods like mashed peas, algae, carrots, cucumber, zucchini broccoli, and lettuce are all ideal snacks.


There you have it guys and gals, everything you need to know about the size and growth rate of Comet Goldfish, as well as how to ensure that they grow big, fast, and strong. They’re some pretty cool critters, not to mention super hardy and ideal for beginner fish keepers.

Photo Credits: Sheffield Tiger/FlickrCC.