What Filter sould I choose? A basic quastion that bothers all hobbyists!

Which Filter to Choose

by Dr. Timothy A. Hovanec

A basic question facing all hobbyists is what filter should I use for my aquarium. This is not an easy question to answer because it depends on many variables.

When choosing a filter one needs to consider the size of the tank, the type and size of the fishes in the tank, and the time one has to maintain the filtration system. I’m sure considering the tank size and fish is something you have read before but how does one’s time factor into the decision? Quite simply, every filter needs maintenance, some more than others, and if you won’t take the time to do the maintenance then the filtration system will become ineffective. The importance of one’s time will be clear with a few examples.

There are many standard types of aquarium filters. Some of the most common are the undergravel filter (UGF), the outside hang-on-tank power filter and the canister filter. Many people would consider these filters to be equals and would recommend any of them as a filter for your aquarium. However, the undergravel filter is not a complete filtration system. Furthermore, the undergravel filter requires regular maintenance just like the canister and power filters. But in reality how many people really maintain an UGF? In fact, how many people know how to maintain an undergravel filter? Now to the long-term hobbyist this may seem like a crazy question but I have talked to many people with undergravel filters who have no idea what a gravel washer is for. As an aside: if you’re reading this column and work in a pet/fish store, I would ask that when you sell a filter, any filter, take a few minutes and go over with the buyer how to maintain the filter. Conversely, when buying a filter ask the sales clerk about how to maintain the filter. This seems like commonsense but my experience tells me that there are a lot of fish aquarium owners that have little clue on how to maintain their aquarium filter.

Consider the time and problems with maintaining an undergravel filter. The goal is to remove dirt from between the gravel on top of the filter plate so that the water can flow freely through the gravel and contact the nitrifying bacteria which colonize the gravel grains. To do this, one has to siphon through the gravel which can disrupt the decorations and planting. You also have to completely remove the light fixture and glass lid to clean the UGF effectively. Add in that one needs to replace the airstones, the air pump diaphragm, clean the inside of the lift tubes and replace brittle airline tubing and this starts to sound like work! This is why I feel that most aquarium owners with undergravel filters, who know better, still don't maintain them. Human nature is such that we put-off those tasks that we don’t like for as long as possible.

Does your thinking that an undergravel filter is your choice for that new aquarium change when you consider the time and hassle factor of maintaining it?


Contrast the UGF with the modern power or canister filter. The hang-on-tank power filters that are available today are engineering marvels when you consider that for less than $70 in most cases, they run 24 hours a day, 365 days a year with little trouble and cost only pennies a day in electricity to operate. One can have a successful aquarium with a power filter as the only filtration system. Service is convenient and takes only a few minutes a month. Plus servicing can be done without having to remove the light fixture or the lid.
In general, hang-on-the-tank filters are for someone looking for an easy to use, effective filter that will need some routine maintenance such as changing the pad. Fortunately, changing the pad is easy for most hang-on filters and takes less than 5 minutes. The old pad is lifted out of the filter and thrown away, a new pad is taken out of the box or bag and slid into the filter. In most cases, the filter does not have to be turned off. How often the pad will need to be changed depends on how much food is put in the tank and the number of fish in the tank. Every once in a while a more thorough cleaning of the filter should be done. This means cleaning the inside of the intake tube, cleaning the impeller and the area where it sits, and cleaning the filter box.

Canister filters are generally more complex than a power filter but they still have many convenient features and can be serviced in 15 minutes or so. The features that distinguish a canister filter from a hang-on filter are they generally contain much more media. Most canister filters can hold 12 to 15 oz of carbon versus only one or two hang-on filters with that capability. In the same aquarium situation, a canister filter will generally run longer between cleanings than a hang-on filter.


The drawbacks to canister filters include the continued reduction in water flow as the filter clogs. As the filter traps dirt, less water will make it through the filter which means a lower flow back to the tank. In extreme cases of filter neglect, the flow back to the aquarium will be completely cut-off. This is in contrast to the hang-on filter which will always pump water back to the aquarium but that water may not be filtered. Cleaning a canister filter is more involved than a hang-on filter. To clean a canister filter it must be taken apart which means dealing with the hoses, valves, pump and other parts of the unit. While not difficult, cleaning a canister filter is more involved than cleaning a power filter.


Which filter you should use depends upon the type of aquarium you plan to set-up and the way you approach filter maintenance. No one filter will be the best for every case, conversely none will maintain water quality if they are not serviced. If you want a simple filtration system for an aquarium that will not be overstocked or overfed and you are willing to do monthly filter maintenance, then the hang-on-the-tank filter is probably the filter for you. Change the filter pads at least monthly and every other month clean the entire unit. The time needed for maintenance is minimal but it must be kept in mind that the system cannot be overwhelmed with fish or food.

If the tank you want to set-up is large and/or is going to have a lot of messy fish then a canister filter is the one for you. African cichlid tanks and goldfish aquaria are examples of aquaria that would commonly be filtered with canister filters. If you are rather lazy about performing filter maintenance (you’ll do it but probably every other month) then a canister filter is a good choice. It will provide a lot of filtration capacity and can be abused more than a power filter.

Finally, to correctly answer the question of which filter is best for your aquarium you have to be honest with yourself. How much time are you willing to allocate to servicing the filter? If the answer is “as little as possible” then get a power filter with easily changeable filter cartridges. If you think the filter is too complicated don’t buy it; you’ll probably not service it often enough. Go with something simpler that you understand. Don’t be intimidated by a sales clerk who is trying to sell you the latest cutting edge filter and don’t, for a second, consider a filter which claims it does not need servicing! Lastly, make sure you understand how the filter works and what you need to do to clean it before leaving the store.

So what filter is the correct one for your aquarium - the filter that you’ll maintain on a regular basis (and don’t forget the partial water changes).