Why Use A Freshwater Sump?


OK, so as I’ve said on many other occasions on this site, I have mainly aimed everything here at people who are new to fishkeeping and aquarium setups. That means, in general, a focus on planted tropical freshwater tanks or other simpler freshwater setups.

We’ve gone over why these are better for beginners in various other articles on this site, so I won’t repeat myself here, but one of the main reasons has to do with the complexity of the marine setup itself. That includes all the special gear and, of course, all the plumbing.

One of the most iconic components of the marine tank has to be the sump, which we never really see on freshwater tanks.

Status Quo? Status No!

Actually, the truth is that plenty of people also use sumps for their freshwater tanks. There is no real reason not to do it, since it’s not a marine-specific technique. Yes, you basically need one to have a good marine reef tank, but many of the benefits a sump brings to marine tanks can also work for tropical aquariums. Don’t believe me? OK, let’s go over some of the main reasons.

I Feel Pretty

By far, the most important reason to have a sump is that it separates all the technical aquarium equipment from the display portion of your aquarium. In fact, that’s a good way to think about it. Your main tank is the “display” tank and the sump is, well, the other tank no one sees.

This let’s you do a couple of things. First of all, it means that you can make a completely natural-looking aquascape. There are no filters or heater to ruin the look you want to achieve. The drainage and inlet ports that lead to your sump can usually be hidden pretty easily. The most beautiful and creative tropical tanks use sumps and just would not be the same with aquarium stuff in the main tank.

Turn Up the Volume

I’ve said this elsewhere, but the more water volume you have, the more stable and easy to manage everything is. A sump is an effective way to add water volume to your aquarium without needing extra space. Remember, the sump usually goes in the cabinet below your main tank. Let’s say that you have a 100-gallon tank with a 20-gallon sump. That’s a 20% increase in your total water volume without having to knock a hole in your wall or saw a piece off the couch.


The other great thing about a sump tank is that you can do water changes really easily – especially if you install a small additional water pump that you can switch on when you want to change water. Just put that pump’s hose in a bucket, pump out the water change amount, and replace it. If you’re smart you can even do both at the same time, by matching the pump’s rate more or less with your tap. Switch on both, wait a few minutes and your change is done, barring the water safety additives of course.



Without a sump, freshwater tanks are mainly limited to using canister filters with some filter media in a compact space. It’s always a fight between the size and capacity of the filter media and how much space you are willing to sacrifice in your display. Well, if you use a sump you can go crazy on the filtration. You can have a huge multi-media filter with a big mechanical filter, gobs of biological filter media, and whatever else you want. This includes water temperature sensors, chemical sensors, and all the other stuff you would have to hide.

Mainly however, you can have more filtration than could ever be possible in the display tank itself, so it makes your life easier and makes your tank life happier too.

Maintain Your Position

Nothing lasts forever and eventually things like pump motors and other doodads will fail. Without a sump this means significant disturbance of your tank life and possibly having to rip up some of your aquascaping. In the case of a sump, you can fix and change out things quickly and easily without your fish being any the wiser. It makes maintenance go from a long chore to a minor inconvenience.

Public Disturbance

I’ve already alluded to this above, but one of the best things about using a sump is that it minimizes the amount of stress you cause your fish by messing around in their habitat. Stress is an insidious killer in your tank. It makes fish prone to disease and can lead to behavior where they hurt themselves or bully other fish. It’s not uncommon to get to your tank in the morning following a stressful event and finding one or two fish that have sadly passed away. Some fish even jump from lidless tanks.

It’s not just the big stuff that you can spare them. Adding things like water safety chemical or medicines to your sump is just another way to keep things out of your main tank which affect the way it looks and ensure the happy daily lives of your fish.

The Downlow

Obviously there are some downsides to having a sump, and since having one on your freshwater tank is optional we should really talk about it.

The main issue basically comes down to cost and complexity. With a sumpless tank all you do is plonk your filters and heaters in the water. The tank doesn’t have wacky plumbing like drainage ducts and overflows. It’s just a tank that holds water. Things go in the top and that’s where they come out. Yes, it’s comparatively ugly, but if you don’t care too much about the ultimate aesthetics you can save a bit of money and effort.