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.
1. Tank Size

Image Credit: New Africa
This is something I hear a lot:
“Can I keep a goldfish in a tank x gallons?”
Look:
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

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.
- Read More: How to Quarantine New Fish
3. Choosing the Best Filter
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.
Sometimes.
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.
Now:
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.
Small.
Inexpensive.
Low-current.
Did I mention these things are super cute?
Pop them in anything from a 5 to 15 gallon tank.
Easy-peasy!
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
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.
Now:
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

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.
Sand
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
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

Credit: 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…
BETTER WAYS.
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.
Conclusion
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!
What kind of dirt or topsoil do you use? ?
Just cheap garden top soil in this tank. I typically prefer the Epsoma potting mix though, sifted first.
But your 2 goldfish in a 3 gallon bowl died soooo
They must of not been happy or healthy is a 3 gallon bowl if they died.
Jake, it is true there was an accident that lead to their decease a good while after writing this article. But fish can die in an aquarium as well; does that mean aquariums kill fish?
Maybe understanding the situation will help you to see that it wasn’t the fault of the home they lived in – in this case, it was my own fault. 🙁
After living in this bowl for nearly a year without issue (water parameters were always 0 ammonia, 0 nitrite and 0 nitrate – a fully cycled bowl), these fish started spawning every 5 days, which lead to their water becoming very cloudy and murky after several weeks. I did a large water change (which I normally don’t do), and like an idiot didn’t plug the airstone back in afterwards. This was a very heavily planted fish bowl (much heavier than I normally recommend) and I KNEW they needed that extra air because live plants produce lots of CO2 at night. In fact, this is a problem that can and has happened in a rectangular aquarium as well. One of my heavily planted 30 gallon rectangular tanks, with only 2 goldfish, also gets dangerously high CO2 levels without supplemental aeration. Admittedly, supplemental aeration is probably more important in a fish bowl than in a rectangular tank, due to the smaller surface area at the top. Anyway, without that airstone, overnight the CO2 levels spiked, and caused suffocation. I blame myself entirely and lest you think I don’t care about my fish, I cried and felt absolutely terrible about the situation. (Many of those who have lost fish can sympathize.)
For what it’s worth, none of my other planted fish bowl setups that maintain proper aeration and a balanced plant ratio have had any fish losses. Mistakes can happen in all walks of fishkeeping. People are quick to jump on bowls as being evil without fully understanding their benefits and drawbacks, as well as what can be done to overcome the latter. In my opinion, the important thing is to actually understand WHY things went wrong so you can avoid them in the future.
In my case, I’m not going to paint with a broad brush and blame the bowl itself when these fish were doing great for so long (so great they decided to have some babies). Rather, I’ve learned the hard way that too many plants without additional oxygen is dangerous to the fish, and not to forget to plug in that airstone after maintenance.
Excellent site
Thank you Tony 🙂
Hi, I just found your site. Very interesting info here. I was wondering. What is a nano or bonsai goldfish? Do they breed tiny goldfish? What breed is the smallest goldfish variety at adult size? Thank you!
I consider a nano goldfish to be a goldfish kept in a smaller aquarium that is either environmentally or genetically stunted. Such a goldfish often does not grow beyond a few inches in length. Breed is generally not as important as these other two factors, as there can be big fish from smaller breeds and smaller fish from bigger breeds depending on husbandry or genetics. Hope that helps 🙂
Do you know if Purigen will remove growth inhibiting hormone like activated carbon will?
Thank you for this website sharing your knowledge, and experience.
Honestly I don’t know, JJ. I would think if it acts like carbon, it might. Personally would avoid it if a smaller fish is desired.
How often do you feed nano goldfish? Does 2-3 times a week + veggies 24/7 sound about right? Should they be fed more or less often when they’re under a year old? Thanks!
For adult goldfish that have mostly stopped growing, I typically feed heavier; 1-2x per day. For younger fish, feeding less often is beneficial for the health of the aquarium and does not encourage rapid growth. But less feeding is best for unheated tanks. Hope that helps. 🙂
How small of an aquarium would you say in humane? I have a ten that has been cycling for 7 weeks that I want to put one or two in!
Some of the oldest fish in the world are a couple of goldies in a 10 gallon 🙂
So I joined the Nano Goldfish FB because I wanted to get information. I only have the space for a little 7gallon tank at the moment. After reading all the rules to joining the group and your article in tank size, I felt comfortable to ask what type of filter I should get… and the first response I got was that the tank I have is too small and was made to feel that I shouldn’t waste my money… so I’ve decided to just come back here to ask you directly. If I have a 7 gallon tank and two small orandas, with a sand substrate and plants like you suggested. What type of filter should I get?
Replied to you on FB but yes the mini sponge filter is ideal for that imo. 🙂
Questions for a goldfish tank – 1. if you are adding a shell you picked up on the beach to a freshwater tank, do you need to do anything to it first besides rinse it (boil it?) since presumably it still has salt compounds on it? 2. can you use found driftwood? 3. If purchasing, is there a type of driftwood you prefer? 4. Can you use slate decorations in a goldfish tank? 5. How do you feel about moss balls in a goldfish tank? Apologies if any of these are silly questions. I just don\’t want to unknowingly introduce any \”toxins\”.
1. No.
2. Yes but soak first for a long time and choose the right wood
3. I don’t purchase it, too cheap 😛
4. Yes
5. Fine but the fish may eat them
Hi,
I have a very new singular black moor goldfish in a tank downward of 10 gallons.
Am I eligible to join the club?
I also really like your articles btw!! 🙂
Thanks,
Of course! 😀