Before we start discussing what type of filter would work for our aquarium and all the nitty-gritty behind maintaining them, we need to expand on the three different types of filtration you get for your aquarium. It can be divided into three categories: Mechanical, Biological, and chemical filtration. In an ideal world and setup, you would need a filter that does at the bare minimum of both mechanical and biological. Since those are the two most important filter methods for your aquarium.

• Mechanical filtration: This is the removal or straining of solid particles from the water, which includes things like fish waste and other waste generated by your aquarium. Unfortunately, mechanical filtration cannot remove dissolved ammonia from the water. Mechanical filters catches and hold particles by physically trapping them within the filter. These would be things like sponges and filter floss. You then remove these and clean them.

• Chemical filtration: This is the second type of filtration. This type of filtration removes waste from the water before they have a chance to decompose, this removes waste products from the water that can no longer be removed by your mechanical filters. Chemical filtration in a way is mechanical filtration on a molecular level. An example of chemical filtration would be Activated Carbon or Seachem Purigen for example.

• Biological filtration:  This is the third type of filtration and arguably the most important in your Aquarium. Biological filtration in an aquarium is achieved by passing water over a medium rich in beneficial bacteria. The beneficial bacteria convert ammonia and nitrites into less dangerous nitrates. These substances, like nitrate, are relatively harmless unless allowed to build up to high concentrations and, therefore, must be removed by doing regular and partial water changes. Examples of biological filtration would be ceramic rings, lava rock, or pumice stone.

Now that we understand the different types of filtration and what they contribute to your aquarium, we can talk about the different types of filters you get in the aquarium trade. There are obvious subclasses of filters that this article won’t be long enough to cover, so I will only cover the “big five”.

• Sponge: The sponge filter is the most basic of all filters that require the least amount of effort to setup and only one point of failure, which would be your air pump. The sponge sits inside your aquarium, with the air pump sitting on the outside. The air pump then pushes the air through the tubing into the hollow space inside the filter sponge. The bubble that rises out of it draws water through the sponge, basically catching debris and dirt that passes by it. And in the process giving beneficial bacteria a place to grow.
• Internal: Internal power filters are designed to be installed inside the aquarium. Not only are they extremely easy to install, but they are also easy to maintain as well. When the filter becomes clogged, simply remove the sponge attachment and rinse with some aquarium water. How it works is the power head pulls the water directly into the filter chamber, which is usually occupied by a sponge. Once the water passes through the filter, the water is pushed out of the outlet of the internal filter.

• HOB: Or Hang On Back filter. And just as the name describes, a HOB filter basically hangs on the side of your aquarium with the filter box and pump hanging outside the tank and the intake tube sits on the inside of your aquarium. Water is sucked up the intake by the pump, passed through all the media in the filter box, and then back into the aquarium via a waterfall-style outlet.

• Canister: One massive advantage a canister filter has over the above-mentioned filters is that it can hold a lot of filtration media. You can fill the canister filter with different types of media. For mechanical filtration, you can add filter sponge material. For biological filtration, ceramic rings, lava rocks, and Pumice stone, you can also include chemical filtration. The power head pulls water into the canister, travels through several trays of filter media baskets, and then is returned to the fish tank via an outlet or spray bar.

• Sump: Sumps are arguably the best type of filtration you can get for your aquarium. The type of filtration is hidden in your aquarium stand or cabinet, you can also hide your heaters and pumps in it. The sump itself is usually just another aquarium or in some cases perspex or plastic. The sump is divided up by using baffle plates and the first section is typically where mechanical filtration takes place, the second is for your biological media and the last part of it is for your chemical filtration. Sumps work via gravity, so water runs into the overflow box and into the sump and passes past all the babbles, and then gets pumped back into the aquarium.

What filter do I need for my aquarium?

Now that we covered the types of filtration and filter types, we can move on to what type of filter is best suited for your needs. This is wholly dependent on the size of your aquarium and the amount of fish you will be keeping in it. Low maintenance filters, like sponge filters or internal filters, work well for aquariums that aren’t overstocked or overfed. But they become ineffective once you get past a certain size of aquarium or when you keep fish that produce a lot of waste. HOB and canister filters are more effective for a tank with fish that produce more waste, as they are more powerful and can hold more media types, but they also require more regular maintenance to keep them running properly. And once you get to massive aquariums you definitely need something like a sump filter as it’s the only filter that would be able to handle the massive volumes of water that big aquariums come with.

How much aquarium filtration do I need?

A good rule of thumb is to select a filter with a flow rate at least three times the volume of the tank. So for example, if you have a 30-liter aquarium you want a flow rate of about 100 liters per hour. Meaning that the filter will cycle the aquarium’s total volume around three times in a single hour. And I would say the more, the better, within reason, of course, you don’t want to blow all your fish and plants away.

When should I be cleaning my aquarium filter?

Just like selecting your type of filter for your aquarium, it all boils down to how much fish you are keeping in your aquarium and how messy they get. Logic dictates the more fish you have, the more you would need to clean your filter, and the reverse is true if your aquarium isn’t stocked heavily. A general rule of thumb I use is if I see the flow of my aquarium filters slowing down, then I know it is time to clean my filters.

How should I clean my filters?

The mechanical filtration, such as filter sponge or filter floss, can be cleaned regularly. But don’t do it with tap water, as the chemicals in tap water are designed to kill any traces of bacteria in our drinking water. Instead, rinse it thoroughly using some of your aquarium water instead. However, biological filtration should not be changed or cleaned at all unless it is absolutely necessary. If for whatever reason it is dirty you can just rinse it off with some aquarium water as the same rules apply to biological media as mentioned above for mechanical filtration. Some biological filtration media, such as ceramic rings, pumice stones, and lava rocks, are designed to never require replacement.

Where should I put my filter in my aquarium?

This is a topic that does not get covered as much as it should, which is where you should place your filter in your aquarium. If you have an external filter like a canister filter or a sump. Then move your inlet and outlet to the exact opposite ends of the aquarium. This means that all the water is pushed across the top of the tank, hits the other end, and returns along the bottom, taking any debris and fish waste towards the filter intake. For a HOB filter, the best placement would be at the back and center of your aquarium. And if you have a single internal filter, place it in the back corner of your aquarium, pointing it to the opposite front corner. As for a sponge filter it really does not matter but putting it in a corner makes it easier to hide it from view. The important thing to take away is to check the flow in your aquarium, is it fully circulating around your tank? Are there dead spots? If there aren’t any dead spots then you are good to go, if there are, then use an extra internal filter or wave maker to remove that dead spot.

Do I need to run my aquarium filter 24/7?

Yes, absolutely, your aquarium filter should be running 24 hours a day. Your aquarium filtration system is not only responsible for keeping the water clean, but also for keeping the beneficial bacteria alive so your fish can survive and thrive in your aquarium. But in fact, they are responsible for creating the necessary water flow as well, which helps deliver oxygen throughout the tank. And without oxygen in their water, fish will quickly die.  If the filter is turned off, even for only a few hours, beneficial bacteria would start to die off. And without the beneficial bacteria in your aquarium, ammonia levels in your aquarium will spike up, ultimately leading to the death of your fish due to ammonia poisoning.

[Editorial Note] Hopefully the above explanation and guide will help you pick the correct filtration system.