Do Goldfish Need a Filter?

After seeing some cool videos of filterless tank setups on youtube, I got to wondering – do goldfish actually need a filter, or would they be happy in a filterless tank as well?

The short answer:

Yes, goldfish definitely need a filter.  Goldfish produce a large amount of ammonia compared to other fish, and they require a filter to keep them from poisoning themselves.  A good rule of thumb for selecting a filter for your goldfish is to get one that circulates your tank 4x per hour.

A goldfish can live over 40 years if kept in ideal conditions.  Do just a few things wrong, however, and you can drastically cut the lifespan of your goldfish.

Think about it:

It’s not uncommon to see goldfish that die after only 5-10 years.  That’s only 25% of their potential lifespan.

And it all starts with the filter:

Why Goldfish Need a Filter

A bit of common wisdom I’ve heard over the ages is that goldfish produce 3 times the amount of waste as a similar fish the same size.

I don’t know if this is true or not, but it provides a valuable lesson that any goldfish owner needs to keep in mind.  That lesson?

Goldfish are seriously messy.

The reason for this is simple:

Goldfish don’t have a stomach.  They just have a length of intestines 2x the length of their body.  (Compare that to ours at 3-4x the length of our body.)

Because of this, they have a hard time digesting proteins, and they’ll poop out their food before it is fully digested.  This leads to a lot of excess waste that will break down into ammonia.

And that’s not even accounting for the ammonia they release directly through their gills and vent.

Because of this, a good filter is critical to keeping your goldfish happy and healthy.  Luckily, getting a filter doesn’t have to be a complicated or expensive affair.  You just have to know the right type of filter to pick.

What Type of Filter is Best for Goldfish?

In a Tank

If your goldfish are in a tank, you have 3 main options for filtration:

The internal filter, power filter, or the canister filter.

  • The power filter is the one that you’re probably most familiar with – hanging on the back of your fish tank with a tube that hangs down into the water.
  • The canister filter is an external filter that looks like a trash can and sits below your tank, with tubes going into your tank to collect and return the water.
  • The internal filter sits inside the water of your fish tank and draws the water through a sponge.

Here is a table with the pros and cons of each type of filter to help you make your decision:

Filter Type Pros Cons
Internal + Low flow, doesn’t agitate the water too much.

– Takes up space in your aquarium.

– Doesn’t filter very well.  Not great for heavy waste producers.

Power Filter

+ Inexpensive

+ Easy to maintain

+ Decent quality filtration

– The intake is right beside the freshly filtered water.

– Not as much filter media as a canister filter.

– Takes up space and can be ugly.

Canister Filter

+ Best quality of filtration

+ Can be hidden in the cabinet below your aquarium

– More expensive.

– More work to clean and maintain than power filters.

My personal recommendation for filtering your fish tank’s water is the canister filter.  These are a bit more expensive, but they will provide your goldfish with the best quality water out of the three. 

The reason for this is that they have the most filter media to run your water through, which provides more room for beneficial bacteria to grow in.

In my opinion, the health of your goldfish is more than worth the extra hassle of cleaning out the filter (which you can do less often with the canister type).

If you’re on a budget or don’t want to maintain a canister filter, a good quality power filter is the way to go. If you’re careful about which one you select, you can get one that still provides very good quality filtration for your goldfish.

(If I was going to buy a filter for my mom’s tank, I’d definitely go for a power filter.)

The key to selecting a good power filter is this:

Make sure you get a filter that has a large volume of filter media.  Don’t go for the Walmart special that has those tiny blue filter cartridges.  Try something like the Aquaclear instead.  (Even if you don’t get that brand, look it up to see what you should be looking for.)

The other thing you need to look for is the size of the filter.

Ideally, you’ll be looking for a filter that can cycle your tank at least 4x per hour.  So if you have a 55 gallon tank, look for something rated at at least 220 gallons per hour.

Once you have your filter, however, you’re not done.

After all, there is one critical, fish killing mistake you need to avoid when cleaning your filter.

Warning: How Not to Clean Your Filter

Once you have your filter, the time is eventually going to come where you need to clean the thing.  This is where a lot of new goldfish owners screw up.


By cleaning the thing too well, or by getting rid of all of the old filter media and replacing it entirely.

A great portion of the beneficial bacteria that clean the ammonia and other toxins out of your water live in that filter media.  Get rid of them, and harmful amounts of waste will quickly start building up in your tank’s water.

At that point, if you don’t take drastic action, your fish are at serious risk of going belly up.

Proper care of each individual type of filter is beyond the scope of this article, but make sure you look up how to properly maintain the type of filter you buy for your goldfish.  Each filter is going to be slightly different, so you want to make sure you’re doing the right thing for your filter.

Your Filter May Not Be Enough

I want to preface this by saying that a filter is absolutely necessary for keeping your goldfish healthy.  What I’m covering below isn’t a replacement for having one.

That having been said, the filter is only one part of the equation.

It can remove what’s already there, but you also want to reduce the amount of waste that’s produced in the first place.

Killing Your Fish With Kindness

The main source of pollution in your goldfish’s water stems from how (and what) they are fed.

Let’s start with the what:

Standard fish foods are high in protein.  This is bad, because your goldfish is terrible at digesting protein.  Compared to other types of fish, you want to be feeding them a lower protein food that they are more easily able to digest.

It may be a bit more expensive per package of food, but it’s an investment that will pay off in the health of your aquarium or fish pond.

Plus, it will actually help you save money.  Here’s how:

You may have also heard the common rule of thumb that you should feed your fish 2-3 times per day what they can eat in 2-3 minutes.  This rule of thumb was probably intended to keep new fish owners from overfeeding their fish.

Unfortunately, it’s actually causing new fish owners to overfeed their fish.

According to Rain Garden Ornamentals (a nursery that specializes in raising goldfish), your goldfish can get the nutrition it needs from the amount of food they can eat in only 30 seconds.

That’s many times less food than everyone else is telling you to give.

Which is much less food that’s going to decompose as poop and pollute your water.

Your goldfish’s carp ancestors were used to foraging for food all day, however, and this reduced feeding schedule will result in them begging you for food they don’t need every time you walk by their area.

Luckily, (since they’re omnivores) there is a simple solution to this.

Leafy greens.  Here’s how it works:

  1. Microwave any leafy vegetable that you would normally eat for a few seconds so that it becomes soft and wilted.
  2. Put it into your tank for your fish to nibble on.

Your fish may turn this down at first, because the processed food is much tastier than eating their vegetables.  Stay firm, though.

If you have a pond, you don’t need to worry about providing them vegetables to forage on, as they can eat the algae and plants that grow on the bottom of your pond.

2 Ways Underwater Gardening Keeps Your Goldfish Healthy

Speaking of plants, this is another great way of providing your goldfish with high quality water.  They do this in 2 ways:

First, they remove waste products from the water.

Above ground, if you were planting a garden, you’d provide it with compost and fertilizer to help your plants grow.  Underwater, on the other hand, the plants are able to grow on just the nutrients left behind by your fish’s waste.  This leaves your plants happy and your water cleaner.

Second, they help oxygenate the water.

Much the same as terrestrial plants take in CO2 and release oxygen back into the air, underwater plants take in CO2 from the water and release oxygen back into the water.  This is another way plants help improve the quality of your aquarium’s water.


There are a lot of things you can do to help give your fish high quality water, but it need not be overly complicated.

If you’re thinking of raising goldfish, absolutely get a filter.

If you already have one, switch your goldfish over to a high quality food, and feed them only what they can eat in 30 seconds per day.  This will significantly reduce the amount of waste they produce, which will reduce the strain on your filter.  (As well as on any other fish in your aquarium.)

If they start begging for food afterwards, don’t give them more food.  Give them some leafy greens instead.

Did I miss anything?  Do you have any other questions about keeping your aquarium clean and healthy?  Leave them in a comment below, and let’s keep the discussion going!