Choosing an Aquarium Filter
For new aquarists, choosing the right filter can be a minefield.
Which is the best brand?
What size do I need?
How many litres per hour should I be looking for?
There are a whole host of questions such as the above that are often asked when choosing an aquarium filter, so in this article, we’re going to answer them and help you on your way to choosing the perfect filter for your setup and budget.
What type of filter is best for my aquarium?
With many different types of filter available, this is often the first question asked when shopping for the perfect aquarium filter.
Choosing an aquarium filter first depends on you identifying which type of filter you require.
Internal filters are a great option for smaller aquariums, though some are rated for larger tanks. Internal filters can be a great choice, they’re small, compact and easy to maintain. I would recommend a good internal filter for aquariums up to 90L in volume. Aquariums larger than 90L would certainly benefit more from a larger filter capacity.
External filters sit outside, usually below, the aquarium. There are many advantages to having an external filter. An external filter will often provide more flow around the aquarium, keeping it visually cleaner. They also offer more space for filter media and allow you to customise the layers of media contained.
HOB filters hang on the back, or side, of the aquarium. The advantage here is that space is saved as the filter is not inside the aquarium. I haven’t personally used a HOB filter, as an external canister offers far more media volume capacity, but I have it on good authority that they work well.
Sponge filters are a great option for some aquariums too. Sponge filters are cheap, easy to maintain and easy to set up. But they do have drawbacks. Sponge filters do not create a great deal of flow, so as an only filter they are only really suited to sparsely stocked aquariums or Betta tanks. However, I do use sponge filters as additional filtration in all my tanks.
When choosing which type of filter to use, tank size, bioload and the type of fish you want to keep are all things to consider.
Aquarium filter ratings
Aquarium filters all come with a rating for the tank size they are suitable for. These, like their flow ratings need to be taken with a pinch of salt.
Aquarium filters are tested fairly unrealistically. Their capacity and flow rate are usually measured whilst the filter is empty with no media in it.
This means that my JBL e1902 which is rated at 1900lph, is probably pushing out more like 1200lph, or less, now that it’s filled with sponges, matrix, micromec and purigen.
So, the flow rating stated in the spec is not the flow rate that you will get. But it is still a fairly useful figure when choosing an aquarium filter.
This is a similar story when it comes to the aquarium size rating is also a little off. Some companies seem to rate their filters more accurate to real-life than others but in general, they all overestimate what their filters are capable of.
A good example of this is my old Fluval FX5. The FX5, like the newer FX6, was rated for aquariums up to 1500 litres.
In reality, it would probably cope with the bioload providing that the aquarium was lightly stocked for its size, however, it would have no chance of circulating that volume of water enough to clear all the debris from the bottom of the aquarium.
I had the FX5 on a 580l aquarium and it needed a bit of help. I had additional wavemakers and sponge filters to help keep the tank clean of detritus etc.
It may now be sounding like I wasn’t happy with the old FX, I was, it was an awesome filter, I’m just pointing out the over-estimations made by companies on their filters.
So, when checking the rated capacity of a filter, bear in mind that the FX5/6 rated at 3500lph is only good for up to around 500 litres, a third of the aquarium capacity that it is rated for. Most filters are more ideally suited to roughly half of the aquarium size they are rated for.
Aquarium filter flow rate
When choosing an aquarium filter, the flow rate is often a big question. How much flow is the right amount?
As we have covered, the flow rates are often overestimated and are a representation of what the filter is capable of whilst empty. But the rating given is a good figure to work off whilst deciding what size filter you need.
There are several factors to think about with the flow rate of your aquarium filter that may affect which filter you choose. Flow rate is not the be-all and end-all of filtration.
The flow rate affects how much the water in your tank is pushed around and a higher flow rate means that debris and detritus are more easily pushed into the filter out of sight.
Whilst this makes the tank look clean, it has little effect on the nitrogenous waste (ammonia and nitrite). In fact, a slower flow rate can often work far better for this and can even help some filter media’ to break down nitrate too.
In general, a filter with a flow rating of 5x your aquarium volume per hour should keep the aquarium looking fairly clean.
I currently have a Fluval Roma 200 setup with an APS 1000EF (rated at 1000lph), plus a sponge filter or two. The filter does a good job and keeps the water very clean. The water is always clear and never reads any ammonia or nitrite.
But there is often debris (bits of plant and general mess) in the bottom of the tank. Ideally, it requires a little more flow to pick these bits up but as this is a breeding tank for the Myrnae, I’m ok with it how it is.
Another tank of mine is around 580L, this tank has a JBL e1902 (1900LPH), an Eheim pro 3 350 (1050LPH) and two wavemakers (9000LPH total), that’s over 20x the tank volume per hour in flow rate, as per the equipment ratings.
The fish have no problem with this amount of flow and it is rare there is any debris floating around in there.
So if you want the aquarium to look clean and be free of any detritus or debris from plants etc then a higher flow rate works well!
That is of course unless you keep fish that require slower flowing water. Some fish do not cope well with fast flow. Fish that originate in slower moving, or still water will not cope well with turbulent water. If you keep such a fish, then a filter with a lower flow rate is a better choice.
This is where sponge filters are ideal. providing that the aquarium is sparsely stocked, a sponge filter can be used. Alternatively, a sponge filter could be used as additional filtration to help a slower flowing filter convert waste.
So, unless you keep a Betta or another fish that likes very slow flow and little water movement, my advice would be to look for a filter that is rated to circulate at least 5x your aquarium volume per hour.
However, the flow rate is far less important than the media capacity. A filter that only cycles through the volume of your aquarium once per hour can be enough to keep your fish healthy and keep the water free of nitrogenous waste, aslong as it is big enough.
Media capacity is one of the most important factors when choosing a filter.
Ultimately, the more media it can hold, the better.
The media inside the filter is what keeps the aquarium clean and healthy. So the more you can get in there, the cleaner and healthier your aquarium will be.
It is also worth looking at how the media stacks up in the filter too. A tall stack of multiple media is more effective than a wider area with only a few layers.
For more on filter media setup, have a look at my previous article, HERE.
The more bio media you can cram into a filter, the clearer your water will be. Bio filtration is far more important than mechanical to achieve crystal clear water.
Just on a side note, there seems to be a common myth that you can ‘over do it’ with bio media. This is not true. Add as much as you can!
What is the best brand for filters?
People often get held up on choosing the right brand of filter. In all honesty, most of the top brands can be relied upon for producing great quality equipment with a good warranty package.
So, personally, I wouldn’t say that there isn’t a single ‘Top Brand’, but I certainly have some tried and tested favourites:
JBL – JBL.de produce some great quality equipment and I love the Cristalprofi range. They’re efficient, effective and stylish. The e1902 is particularly impressive with 6 layers of filtration.
Eheim – Eheim products are of great quality and do an amazing job! The Eheim professional range is up there with my favourites.
Fluval – Fluval also produce great quality equipment and their FX range are some of the most powerful filters on the market.
All pond solutions – All pond solutions are great value for money. They are not the greatest filters going, but at the price that they are sold at they are an absolute bargain for a fish keeper on a budget.
Ultimately, the best brand of filter is the one that works best for you.
You will find all of our top recommended filters in our ‘Shop‘.
What is your favourite filter? Let us know in the comments!!! Happy Fishkeeping!