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Canister filters have long been the go to filtration option for larger tanks in the freshwater world, but are they good for saltwater tanks too? Lets Find out!

Today we are looking at canister filters and their applications in Marine Aquaria, but lets first take a look at how they work. Canister filters at their core are very simple. They incorporate several baskets for different types of filter media, and a small circulation pump housed inside of a compact case. Once an initial siphon is created, the pump draws water from the tank through the inlet tube. It then passes through several stages of mechanical, chemical, and biological filtration. Once it reaches the end of the canister the water hits the pumps and is returned to the tank via the outlet tube.

One of the biggest issues that canister filters come with is that they can be tough to clean out. As with all aquarium equipment, a canister filter will slowly collect waste and detritus meaning that it will need to be periodically cleaned. Unfortunately, canisters are filled with water and don’t really have a great way of draining it. Depending on the model that you have, most filters will have a way to lock the inlet and outlet to maintain the drain siphon while still allowing you to move the filter away from the tank. First things first, you will need to unplug the filter to stop the filtration pump. Next just unlock and remove the inlet and outlet tubes. Take the now disconnected canister to a sink, outside, or where ever you choose to do equipment maintenance. From here you can drain filter and remove the media. Double check your mechanical and chemical filtration and replace it if need be. Aso take a look to see if your biological media has started to collect waste. If its has gotten too dirty take either the water that you drained from the filter or some newly mixed saltwater and rinse the media in it. Make sure that you clean the biological media in saltwater otherwise you will kill the bacteria that colonized it. While you have the filter open and empty rinse out the body and make sure it’s clear of debris. Once everything is clean replace the media and hook the canister back up to your tank. It's also a good idea to have some new water mixed up as you will need to replace whatever you drained from the filter initially.

So why do canister filters get a bad rap when it comes to saltwater tanks? Well in fish only situations you can certainly put a canister filter to use when used alongside a protein skimmer. Unfortunately this isn’t the case for reef tanks.

Once you add coral to a tank it makes everything a bit more complicated. First off, coral are sensitive and need water that is both pretty clean, and very stable. Unfortunately, canister filters just don’t measure up to how sumps perform in these areas. First, sumps will hold much more water than a canister, greatly adding to your total system volume and keeping your parameters more stable. Second and also due to the lack of size, there simply is not enough surface area in the canister for bacteria to grow when compared to a sump. This can be combated by filling it primarily with biological media, but even then there may not be enough space to make up the difference.

As fish are a little less picky than corals, a canister filter is likely a better fit for FOWLR tanks. Keep in mind that you will still need to perform regular maintenance on it and replace your media on a schedule, otherwise you risk letting it become a nitrate producing factory. Despite these issues, canister filters can still definitely be used on Marine Aquariums, but are often best saved for Nano tanks where a sump just isn’t practical.

Outside of being a permanent filter for your tank, canister filters do have a number of other uses in the hobby. We have highlighted a few of them in the video linked in the cards but I’m sure you can think of a few more if you get creative.

Here at MD we carry a variety of canisters from Eheim, Fluval and ZOO-Med that are great for both saltwater and freshwater applications. They all get you to the same endpoint, but each one has different features which may appeal more to you.