Affordable, convenient, inconspicuous – the hang on back filter excels at all three.
The hang on back filter (sometimes abbreviated to HOB filter for short) is the most common filter you’ll find in pet stores and online. A small pump pushes water into a compartment stuffed with filtration media, and then back out into the aquarium.
Sometimes referred to as the all-in-one filter, as it can accommodate mechanical, chemical and biological filtration. They are affordable and easy to conceal behind the aquarium.
The biggest problem has been that because they are so small, most HOB filters available on the market rely on a high water turnover to run efficiently (causing strong current in the water which can be stressful, especially to fancy goldfish breeds).
But good news:
The Fluval C model takes delicate fish species into account by adding a special wet/dry trickle chamber that can hold nitrate reducing filter media (which also provides a greater surface area for beneficial bacteria).
The trickle chamber allows the media to be exposed to oxygen and water at the same time so it can work much better than submerged media. And the design of the filter allows you to turn down the flow without compromising the efficiency.
It is unlike any models available on the market and the only one I recommend for fancy goldfish keepers or any delicate fish.
If it were me, I would PACK every square inch of this filter with FilterPlus or Seachem Matrix, which can assist in nitrate removal and provide more surface area than any other media I know of.
Using the Fluval prefilter sponge on the intake of the filter is a really good idea, as it can reduce the time between filter cleanings and prevent nasty mulm buildup in the media which can make your fish sick.
Don’t let anyone tell you Undergravel filters are outdated.
When set up correctly, these things can be AMAZING at filtering your goldfish aquarium.
You have a surface area for your beneficial bacteria that is literally as huge as the bottom of your tank, something no other filter can match. That means a safer environment for your goldfish.
Traditionally, the UG filter is positioned under a layer of gravel at the tank bottom and pulls debris through the gravel bed. However, goldfish shouldn’t be kept with gravel (it’s a choking hazard), and with this setup you can get a lot of poop trapped at the bottom, which can be hard to clean and bad for your tank’s environment.
But there’s a workaround:
Instead of pea-sized gravel, you can use hydroton, nitrate reducing filter media like Pond Matrix (comes in a 1 gallon size) or small pebbles (bigger than the fish’s mouth, though does not support nitrate reduction).
And instead of pushing waste down into the filter bed where it gets trapped and yucky, you can force it up the opposite way with a pump and use a prefilter on that pump to trap the debris, making cleaning so much easier.
Marineland’s powerhead offers the ability to easily reverse the flow for your Undergravel filter. You can also attach their prefilter to it to prevent waste from entering your filter bed.
Simply connect the pump outlet tube to your riser tube with a reverse flow and enjoy a safer and more effective aquarium filter.
The canister filter provides a powerful filtration option. These filters operate by running water from the aquarium down to the filter underneath and then back up into the aquarium.
They can hold a LOT of filter media and don’t take up room inside the tank, giving your fish ample swimming room. And if you don’t want a filter that’s intrusive, a canister could be a great option for you.
They are great for spaces where you want something quiet, such as in an office.
This one by Penn Plax gives you everything a canister filter should, while remaining affordable. A big plus is the flow rate shutoff valves so cleaning is easier (a big complaint for most canister filters).
With canister filters, you’ll probably want to make sure you use a spray bar to distribute the current.
There are two main kinds of wet/dry filters: above the tank and under the tank. For above the tank setups, water is pumped from the tank into a tray situated above the tank and trickles over the different layers of filtration media. Like canister filters, what is inside is totally up to the aquarium owner. There are DIY versions, though these never seem to look very nice.
But this brand has a clean design and is very customizable.
Durable sponge does not disintegrate over time when squeezed
Provides aeration to the water
Gentle current perfect for delicate or baby fish
With superior surface area for bacteria to grow, sponge filters work by pulling water through the sponge with the help of an air pump attached to airline tubing and making a home for beneficial bacteria in the little sponge holes.
They are great for tanks with fry or small baby fish, as they won’t suck up young ones and provide a gentle current.
It’s a simple and affordable option, though it does require frequent cleaning to work well and does not support nitrate reduction.
I like to use them alongside a more powerful filter for a biological boost and increased aeration in the water.
This one is good for tanks up to 75 gallons in size.
Do Goldfish Need a Filter?
The truth is, goldfish need to have a filter, and you need to have one for your own sake as well.
Goldfish produce toxins (through their waste and respiration) that accumulate in the aquarium and can cause all kinds of major problems.
The purpose of a filter is to supply a multi-pronged approach to get rid of the nasty toxins and keep your goldfish safe using a combination of mechanical, biological and sometimes chemical filtration.
Theoretically, goldfish could live without a filter on one condition:
Huge daily water changes.
Those would effectively remove the toxins and keep the water safe for our finned friends.
But it isn’t practical for most people to be doing this for their aquariums! We have things to do besides carrying buckets all the time and paying a massive water bill.
Filtration stands in the gap between a dirty tank and going crazy with water changes.
It’s the missing link!
What kind of Filtration is Best for Goldfish?
“Think of your goldfish filter as a mini sewage treatment plant.” – Goldfish keeper
There are 3 things to consider when it comes to picking out the best filter specifically for your goldfish.
Common filter options like hang on back filters and canister filters hold less media.
That’s why everyone is always hyping having a high volume of water flowing through them, because without it there isn’t enough oxygen to keep the bacteria alive.
But guess what?
While athletic breeds like Common and Comet goldfish don’t mind current, fancy goldfish don’t like a strong current in the water.
Their fins are longer and catch the water current, blowing them around the tank or causing them to struggle to stay in place.
Sometimes they give up the fight and hang in a corner or sit at the bottom. This STRESSES the fish which weakens their immune system.
And what does a low immune system lead to…?
Many filters are designed in such a way that they require frequent cleaning to stay clear of debris.
If debris is allowed to build up in a filter, in certain conditions it can become incredibly toxic.
Mulm (white gunky gross buildup) and sludge (brown gunky gross buildup) stress the immune system as they become loaded with bad bacteria, leading to sick fish.
Filtration is more than just trapping particles of fish poop or having clear water (though those are nice of course).
Filtration is about completely eliminating ammonia (the #1 killer of aquarium fish in the world) and nitrite, turning it into the much safer nitrATE.
To get rid of ammonia you need beneficial bacteria that consume it and turn it into a far less harmful substance. A good filter has got to have lots of room for beneficial bacteria to grow – or it they can’t do their job.
Let’s face it:
The majority of filters on the market today are way too small to be effective for our “messy goldies.”
They just lead to a false sense of security for the hobbyist.
So choose one of the high performing brands above for best results.
What kind of filtration you choose depends on your lifestyle, the kind of fish you own, and the needs of your aquarium as a whole.
There is definitely a trade-off with the more discreet filtration systems being not as efficient or safe for the fish, and the more powerful ones being more expensive or visible.
My advice has been and always will be put the fish first, then worry about looks afterward.
What is best for your pets?
In the end, a healthy, well-filtered aquarium will support healthy, happy goldfish and save you extra work.
What Do You Think?
Do you wonder if your goldfish have enough filtration to balance out your water changes?
Have a question about how a certain filter works, or a preference for your tank?