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5 Basics of Nano Goldfish Keeping (With Pictures)

Lindsey Stanton Profile Picture

By Lindsey Stanton

goldfish in bowl

Hey, you with the small aquarium.

(Yeah, you.)

Finding it hard to get some decent basic help with your setup?

Never fear.

You’re in the right place.

The 5 Basics of Nano Goldfish Keeping

1. Tank Size

small goldfish in goldfish bowl
Image Credit: New Africa, Shutterstock

This is something I hear a lot:

“Can I keep a goldfish in a tank x gallons?”


If you’ve read my post on tank size and why there are no scientific-based rules…

… You know it comes down to 2 things.

Your water quality and swimming space.

That said:

I’ve kept a couple of 2.5″ goldies in a 3 gallon.

Water quality remained perfect.

(They were so happy they even spawned!)

Each situation varies though, so sometimes you might have to reassess your filtration if you find that you have chronic ammonia or nitrite problems.

You might have to add an airstone to make sure they all get enough oxygen.

The bottom line?

It can be a bit of trial and error until you find what works for you.

There is no “one-and-only” right way.

But that’s the beauty of goldfish keeping – there’s always an experiment to do!

Here’s the takeaway:

Please don’t get hung up on this.

Or let other people make you feel bad.

Focus on what really matters – proper feeding, water quality, and creating a balanced environment for your pets.

(That’s just my $0.02.)

2. Quarantine

goldfish in bag
Image Credit: Alex Violet, Shutterstock

Don’t miss this:

When you get new fish, it doesn’t matter how big or small the tank is going to be…

You’ll still need to quarantine. 

A lot of people overlook this or think they don’t need to do it if they only have one fish or several new ones.

But it’s important.

Especially if you don’t want your fish going belly-up after a couple of months from untreated disease.

Let’s face it:

MOST goldfish come diseased (typically with parasites).

Unless you buy from a very trusted source, such as a breeder or importer who does a full quarantine.

You usually need to clean them up if you want them to live a long time.

Quarantining is what you should do right off the bat any time you’ve got a new fish.

Very important.

If you're terrified of passing on any bugs your new fish may have to your entire aquarium, or just want to be sure you do the quarantine process right, we recommend you read our best-selling book The Truth About Goldfish before you put them in.

The Truth About Goldfish New Edition

It has detailed instructions on a seamless quarantining process and so much more. Your fish will thank you!

3. Choosing the Best Filter

aquarium sump

Okay, let’s jump into filters.

Let me point out the obvious:

In a small tank or bowl, you’ve got less room for filtration.

But don’t panic:

There are LOTS of options!

Just because your aquarium is small doesn’t mean it has to be dirty.

Chemical Filtration

Chemical filtration means you use carbon (aka charcoal) or resin like Purigen in the filter to remove ammonia and nitrite and remove heavy metals from the water.

It also makes the water stay fresher much longer than without.

Using carbon cartridges CAN work long-term…

… But the fish might outgrow the tank.

This is because the carbon can remove growth inhibiting hormones.

They usually rely on power filters to work.

In a small tank?

This can lead to WAY too much current.

As long as you’re able to get the current down, it can still be a viable option.

So I personally prefer to use biological or plant filtration on small tanks.


It depends on the situation, honestly.

I usually use it in an uncycled or temporary tank, such as hospital/quarantine.

But to each their own (as they say).

Biological Filtration

Biological filtration relies on one thing to start growing:

Surface area.

Cycling the filter before you add the fish helps your tank be stablized beforehand.

You would do this just like you would in a normal tank.

I’ve even cycled a fish bowl!

The process is the same.


You don’t absolutely HAVE to cycle first.

You can do what’s called a “fish-in” cycle.

Or you can use live plants alongside your filter in something like a dirted tank (more on that later).

Option 1: Sponge Filter

Fine-porosity mini sponge filters are an excellent choice.




Did I mention these things are super cute?

Pop them in anything from a 5 to 15 gallon tank.


You can use it alongside your existing filter for a big biological boost.

Or just by itself.

Option 2: Seachem Matrix

Seachem Matrix has amazing surface area, way more than regular gravel.

You can use this stuff in pretty much any filter with a chamber.

Box filter…

… HOB filter…

… Undergravel filter…

There are TONS of possibilities.

Plant Filtration

dwarf hairgrass aquatic plant
Image Credit: muaiyayo, Shutterstock

Let’s be clear here:

Filters powered by electricity are a relatively new invention.

If people couldn’t keep fish without them before the last 50 or so years…

… Or if it was too much work…

… They wouldn’t have kept them.

And we probably wouldn’t have many of the fish we have today in the hobby.

So, you probably know that without something to remove the waste byproducts a goldfish produces – they can poison themselves.

Before the modern filter craze, people used PLANTS.

(And not plastic ones )

Healthy, growing live plants do much more than just look pretty.

They purify and oxygenate the water.


A lot of people are intimidated by the thought of live plants.

But in my experience, they’re easier to keep than goldfish

And goldfish really enjoy the shelter and natural environments plants help create.

The key with live plants is you need enough (but not too much) for them to do their stuff and balance the tank.

Many kinds of plants can work, but not all types are good options for a plant-filtered tank.

Some plants are too slow-growing to be of much help.

(Yes, I’m looking at YOU, Anubias!)

Vallisneria is almost always a winner.

It’s been used in the past to help revive fish that were struggling with poor water quality or oxygen deprivation.

And it’s too tough for goldfish to eat.

Doesn’t need a ton of light either.

Elodea is also a great plant.

It doesn’t require substrate and looks quite beautiful with its whorling leaves.

Bigger goldfish sometimes enjoy mischievously eating the new shoots…

… But the plant generally grows too fast for that to be a problem.

And if your goldfish are little?

They probably won’t eat on it at all. 

I’ve found that stuff can grow in just about any condition.

Okay, there are a LOT more plants I could talk about, but those are just a couple of examples to get your gears turning.

Plants will almost always grow better when planted in a nutrient-rich substrate.

That’s why I love using soil as a base in my planted setups.

Yes – dirt!

Capped with gravel or sand.

And bada bing, bada boom:

Your aquarium will be a jungle in no time!

4. Choosing Substrate

goldfish gravel substrate
Image credit: Pixy

Now it’s time to pick out your substrate!

There are also many options for you.

It’s up to you.

Capped Soil

My preference for nano tanks is a dirted tank (1″ of dirt) capped with gravel or sand (1-2″) so the plants can grow.

The dirt instantly starts the cycle (and in some cases eliminates it altogether).

Plus it is way less maintenance – no vacuuming anymore, woohoo.

But that’s just me.

There are MANY great substrate options, it’s just what you prefer.


You can do sand only, about 1/2″.

That works fine too, and it’s very easy to clean.

Goldfish love to forage in this.

No choking risk either!

Unless you do a deep sand bed, you’ll probably need to vacuum it at least 1x weekly.


Gravel only is pretty popular.

The good news is with nano goldfish tanks, the goal is usually to keep a “bonsai” goldfish that doesn’t get huge.

So slightly oversized gravel is fine and they won’t choke on it.

Expect to vacuum/rinse out the gravel at least 1x weekly.

Bare Bottom

Bare-bottom is also an option.

It can be very easy to vacuum.

No digging in it for the fishies though

If you choose not to dirt your tank, you can go with plants that don’t require substrate OR pot the plants (muahahaha, shortcut!)

5. Maintenance & Water Changes

dirty golfish tank
By: Chaikom, Shutterstock

Okay so let’s talk about maintenance on your nano tank.

It’s pretty simple.

In most cases, go by the water parameters.

  • Ammonia and nitrite should always be 0. More than that can be dangerous to the fish’s health.
  • The pH should be around 7.4 and not be allowed to dip (tip: used crushed coral or sea shells to prevent it from sagging).
  • Nitrates shouldn’t go past 30ppm. Once your tank is cycled or established, you usually end up worrying about nitrates only.

If you ever have ammonia or nitrite?

Water change time…

… Or throw some charcoal in your filter.

Now we come to an important nano question:

“How do you balance fish growth with water changes for nitrate reduction/tank maintenance?”

Glad you asked.

Because as you have probably heard me say, water changes removes growth inhibiting hormones produced by the fish.

But water changes also removes nitrates, so that’s why a lot of people think you have to do them – and now you have a conflict going on between growth and tank health meaning small tanks should be banned.

Don’t panic:

There are other ways to manage nitrates!

In fact…


Personally, I feel water changes really zaps the joy out of goldfish keeping.

And with a lot of tanks, I used to spend my entire weekend just doing maintenance – a slave to my fish!

Not anymore.

Using live plants, dirted tanks, deep sand beds or special porous filter media are all things you can try.

Sometimes it takes a bit of experimenting…

… But the workload reduction is totally worth it.


Sorry if this was kinda long-winded.

(Do you get the sense that I could talk about this stuff all day? haha)

I hope this post helped give you a foundation for nano goldfish keeping.

So, what do you think?

Have something you want to say?

Leave me a comment!

Featured Image Credit: DJ Srki, Shutterstock

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