I work in a pet store, and if you asked me which product comes back across the counter most often, I would not have to think about it. Fish filters. And here is the thing: they are almost never actually faulty.
They come back because they were set up wrong, because the impeller is clogged, or because someone rinsed the filter media under the tap and killed everything living in it. So this is half a buying guide and half a guide to not ending up in that returns queue, because the best filter in the world will still fail if it is looked after the wrong way.
At home I run a 40 litre indoor pond with a betta, bristlenose and tetras, plus four shrimp tanks, and I use Marina and Aqua One filters.
For most home tanks under about 75 litres, a simple hang on back or internal filter is all you need. My favourite is the Marina Slim, because it is super easy to look after and to change the cartridge, and it is the one I recommend at work. Aqua One internal filters are a solid Australian alternative. Tanks over about 100 litres are better on a canister filter. Whatever you buy, clean the impeller regularly and rinse the media in old tank water, never under the tap, because tap water kills the good bacteria.
For a small to medium home tank, I would buy a Marina Slim filter. It is the filter I recommend most at work because it is so easy to look after: the cartridge slides out, the impeller is easy to get at, and there is very little to get wrong, which matters when you are new to this.
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| Filter type | Best for | Rough price | Watch out for |
|---|---|---|---|
| Hang on back (e.g. Marina Slim, AquaClear, Seachem Tidal) | Most tanks 20 to 100 litres | $45 to $180 | Needs a gap at the back of the lid, can be loud if water level drops |
| Internal (e.g. Aqua One Maxi, Marina i25) | Small and medium tanks, tanks without a lid gap | $30 to $70 | Takes up space inside the tank |
| Sponge filter | Shrimp, fry, bettas | $10 to $30 plus an air pump | Gentle, but does not polish water as well |
| Canister (e.g. Aqua One Aquis, Fluval 207) | Tanks over about 100 litres | $185 to $280 | Most expensive, more parts to look after |
The Three Reasons Filters Come Back to the Shop
1. The impeller is clogged. This is the most common issue I see. The impeller is the little spinning magnet that actually moves the water, and over time it gets wrapped in hair algae, plant bits and gunk. The flow drops, the filter gets noisy or stops, and it looks broken. Pull the impeller out, clean it and the chamber it sits in with an old toothbrush, and nine times out of ten the filter is back to normal.
2. The media was rinsed under the tap. The sponge or cartridge in your filter is not just catching muck. It is home to the bacteria that turn fish waste into something less toxic, and that is the most important job your filter does. Australian tap water is treated with chlorine or chloramine, which kills those bacteria. Rinse the media in a bucket of water you have just taken out of the tank during a water change, give it a squeeze, and put it back. It should still look a bit grubby. That is fine.
3. It was set up wrong. The intake is not fully under the water, a hang on back filter was not primed, a part was left in the box, or the filter is far too small for the tank. A filter that is struggling in a tank twice its size will look like it is not working.
Why I Recommend Marina
I prefer Marina filters, and they are the ones I recommend in store. They are super easy to care for and to change. For someone with their first tank, that ease matters more than any extra feature, because a filter that is easy to clean is a filter that actually gets cleaned.
The Marina Slim hangs on the back of the tank and the Marina i25 sits inside it. Both are cheap to run and replacement cartridges are easy to find.
Aqua One: The Australian Option
Aqua One is an Australian brand and their gear is everywhere in local shops, so parts and spares are easy to get. Their Maxi internal filters (101F, 102F and up) are simple, reliable and quiet, and I use Aqua One gear at home as well. For bigger tanks, their Aquis canister filters are a solid choice, and the replacement impellers and pads are easy to find, which is not true of every brand.
Do Not Throw Out All Your Filter Media at Once
Cartridge filters often say to replace the cartridge every month. If you throw out the whole cartridge every time, you also throw out most of the bacteria living in it, and the tank goes through a mini crash afterwards. That is a classic cause of the fish dying a few days after the tank was cleaned.
Rinse cartridges in tank water and only replace them when they are actually falling apart. If you have more than one piece of media, never replace them all on the same day. Adding a little bag or basket of long life biological media, like Seachem Matrix, gives the bacteria somewhere permanent to live that you never need to throw away.
How Big a Filter Do You Need?
The rule of thumb is a filter that turns the tank volume over about four to six times an hour. So a 60 litre tank wants something rated around 250 to 360 litres an hour. Manufacturer tank ratings are usually a bit optimistic, so if you are between two sizes, go up one.
The exception is fish that hate current. A betta in a tank with a strong filter will spend all day fighting it, which is why I am careful with flow in my pond. Turn the flow down if your filter allows it, or baffle the outlet. Shrimp tanks need a sponge over the intake so babies do not get sucked in.
A Simple Filter Routine
- Every water change: squeeze the sponge or rinse the cartridge in the old tank water you just removed.
- Every month or so: pull the impeller out and clean it and its housing.
- Every few months: check the intake tube and the outlet for build up, and clean them with a pipe brush.
- Never: rinse the media under the tap, or replace every piece of media on the same day.
Two Things to Watch With No Lid
I run my tanks without lids because I like the look. The trade offs are that fish do jump, and water evaporates insanely fast. That second one matters for filters: when the water level drops below a hang on back filter’s lip, it gets loud and can run dry. Top up often. And if you have a lot of open water in one room, keep an eye on the humidity. I had a mould problem in my room from my tanks and fixed it with a dehumidifier and open windows. It is not worth sacrificing your health over.
What I Would Buy
Filters and filter gear I would put my name to. (these are affiliate links)
Want to see everything I run? Here is all the gear I actually use across my reptiles, tanks, rabbits and caique.
Frequently Asked Questions
What is the best aquarium filter for a beginner in Australia?
For most beginner tanks under about 75 litres, a Marina Slim hang on back filter. It is the one I recommend most at work because it is so easy to clean and to change the cartridge, and an easy filter is one that actually gets looked after. Aqua One Maxi internal filters are a good Australian alternative if your lid does not leave room at the back.
Why has my aquarium filter stopped working?
Most of the time it is a clogged impeller rather than a broken filter. Unplug it, take the impeller out, and clean it and its housing with an old toothbrush. Also check that the intake is fully underwater and that the water level has not dropped below a hang on back filter’s lip. Filters are one of the most returned items at the store I work in, and they are almost never actually faulty.
Can I rinse my filter sponge under the tap?
No. Tap water in Australia is treated with chlorine or chloramine, which kills the bacteria living in your filter media, and those bacteria are what keep your fish alive. Rinse the sponge in a bucket of old tank water during a water change instead. It should still look a little grubby afterwards.
How often should I clean my aquarium filter?
Give the media a gentle rinse in tank water at most water changes, and clean the impeller roughly once a month. Only replace cartridges or sponges when they are actually falling apart, and never replace all your media at the same time, or you can crash the tank.
Do I need a canister filter?
Only for bigger tanks, roughly 100 litres and up, or heavily stocked tanks. They hold more media and are quieter, but they cost $185 to $280 and have more parts to maintain. For a typical home tank a hang on back or internal filter is plenty.