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DIY Sump for 90 Gallon Aquarium
DIY Sump for 90 Gallon Aquarium

I built a DIY sump filter for my 90 gallon freshwater aquarium using a standard Aqueon 20 long tank. There are a lot of great advantages to using a sump filter, especially on larger systems. A sump can hold several times more filter media than a hang on back or canister filter. Sumps also allow you to remove equipment, like heaters, from the display tank so that it is out of sight. Finally, since a sump can technically be any container that holds water, there is a lot of room for customization.

Overflow Plumbing

Gluing the Overflow Plumbing
Gluing the Overflow Plumbing

This system is using an Eshopps Eclipse (Medium) overflow, which requires drilling a hole for a 1.5" bulkhead. The overflow has two 1 inch bulkheads, which allows for a Herbie style overflow setup. With this configuration, the primary overflow valve is set partially closed, so that the water level in the overflow box rises to the top of the red secondary, or emergency, standpipe.

Herbie Drain
Herbie Drain

The partially closed ball valve limits the flow through the strainer, maintaining a siphon that runs quietly. A small amount of water flows down the open emergency standpipe. This configuration is popular in reef tanks for its quiet operation and ability to handle a lot of flow without worrying about a clogged strainer causing the display tank to overfill.

Sump Design

This sump is built from a standard size Aqueon 20-long, with three glass baffles siliconed in place to create the different sections. The first two baffles force water flowing into the sump down through the mechanical media and then up into the second section. The third baffle sets the minimum water level in the sump at about 6", or half the height of the tank. This leaves room for roughly 9 gallons of water to overflow from the display tank into the sump in the event of a power failure or pump failure.

Empty 20 Gallon Sump
Empty 20 Gallon Sump

Egg crate style lighting diffuser creates dividers that hold the media in place and keep it off the heaters. I cut sections of the lighting diffuser down using wire snips, and attached the pieces to each other with zip ties. The first section has a platform that holds the media up above the bottom of the first baffle.

Lighting Diffuser Platform
Lighting Diffuser Platform

The second section of the sump holds the bio media and heaters. Here I made a platform for the media to sit on, as well as a divider for the heaters. I also made an air driven circulation device using an old sponge filter housing without the sponges. The two intake tubes sit on the glass bottom of the sump below the diffuser, pulling water from the bottom up to the top of the media. The idea was to create more movement across the media and oxygenate the water before it gets returned to the aquarium.

Circulation Lift Tube Installed
Circulation Lift Tube Installed

Filtration Media

This sump is using a combination of polyester quilt batting, thick sponges, bio rings, and lava rock for filtration. Water flows from the overflow pipes into a basket that holds a layer of polyester batting, which catches most debris and fine particles before they get into the rest of the sump. I covered how cheap and awesome quilt batting is as a filter media in my post about DIY filter hacks.

Polyester Batting
Polyester Batting

The bottom of the filter basket is lined with a 1 inch think coarse sponge. This traps debris the batting didn't catch and allows the water to drain evenly through the sides and bottom into the 3 inch layer of sponges below.

Mechanical Filtration Basket
Mechanical Filtration Basket

In the second chamber is 7 pounds of lava rock, with 4 one-pound bags of bio rings on top. Lava rock is highly porous and often used in pond filters because it is cheap to buy in bulk. I picked up a 7 lb bag for less than $10 at a home improvement store. I got the bags of bio rings, as well as the coarse sponge for the filter basket, from aquariumcoop.com.

Biological Filtration
Biological Filtration

The heaters are positioned in front of the bio media so they are easily visible and accessible if I need to make an adjustment. The final chamber houses the pump, which sends the water back up to the display. This section has extra space I can use to add activated carbon, purigen, or any extra media I may want to cycle.

DIY Sump in Service
DIY Sump in Service

The entire build for this DIY sump cost me under $100, not including the submersible pump ($20) and overflow ($110). Compare that to canister filters like the Fluval FX4 that, while effective, run well over $250 and provide virtually none of the advantages of a DIY sump.


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Having adequate filtration is a key component to keeping your water clean, both aesthetically and for the health of your fish. You don’t have to spend a lot of money to get a lot more performance out of your existing filters. Using some of these DIY aquarium filter hacks, I’ve been able to keep very high stocking levels in my planted tanks, which allows me to grow out more fish. I've had 50+ guppies growing out happily in a well-filtered 20 gallon aquarium. Using cheap materials you can double or triple the filtering capacity of any filter (although I’ll focus primarily on hang on back (HOB) filters here).

Check out my review of the best HOB filters on the market

First, a very quick summary of the 3 types of filtration.

    1. Mechanical filtration is when a material catches debris as water passes through it.
    1. Biological filtration is the process of bacteria that have colonized the filter media converting toxic ammonia from fish waste into less toxic nitrites, and then into nitrates. Nitrifying bacteria can only live on surfaces in an aquarium, so the best biological media has a very high surface area. This is the key to supporting high bio-loads.
  1. Chemical filtration is the process of using a chemical to absorb or neutralize toxic ammonia, heavy metals, or medications in the aquarium. Activated charcoal is the most common example. I don’t use chemical filtration in any of my tanks unless I am trying to remove a medication or other contaminant, so that will not be a part of this discussion.

Hack # 1: Intake Sponges

intake sponges - DIY Aquarium Filter Hacks
intake sponges

Intake sponges can be purchased in large packs online, and are sometimes even carried in the mega-mart pet stores. These are the easiest way to get more filtering capacity out of any filter. I have an intake sponge on every single filter in my fish room. Buying in bulk each sponge cost me under $3. They slide over the end of the intake stem so that water must pass through the sponge before entering the filter. This provides several benefits.

First, the sponge acts as a mechanical barrier that traps larger debris before it enters the filter. Sponges can be easily cleaned by squeezing them out in a container of old water from the aquarium. This keeps fish waste, excess food, and plant debris from entering your filter and potentially clogging up the impeller or gathering in the bottom.

Second, the intake sponge provides biological filtration due to its high surface area and the constant flow of water moving through it. Most of the commonly sold HOB filters come with a single thin sponge to act as the biological stage. Adding an intake sponge can instantly double your biological filtering capacity!

Third, if you’re a shrimp keeper like me, or you breed and raise young fish, the intake sponge is an absolute necessity. Shrimp can graze on the biofilm and debris that gets caught by the sponge, and even very small fry won’t be sucked up into the filter to meet their demise. The photo below shows the intake on a breeder box used in my guppy rearing tank, which also houses a thriving colony of neocaridina shrimp.

Sponge on breeder box intake
Sponge on breeder box intake

Hack # 2: Water Polishing Filter Floss

For several years I routinely purchased OEM filter pad replacements, not realizing there was a cheaper, superior, more customizable solution available. 

What is this water polishing panacea? Polyester quilt batting - AKA filter floss. This stuff is available all over. Google it. You can buy a huge roll for roughly $20 that will last a long, long time. Cut into strips 6” wide by 24” long, a 72” x 90” roll will give you 45 filter floss refills at a cost of under 50 cents each.

I take quilt batting and cut it into strips about 6” wide and 2 feet long, then wrap it around the filter pad frame that came with my HOB filter. This stuff catches almost all of the tiny particles that the intake sponge didn’t capture. The result is crystal clear water. I change it out every 2 weeks, or when it’s brown and gunked up.

Quilt Batting (new)
Quilt Batting (new)
Quilt Batting - as installed (used)
Quilt Batting - as installed (used)

You can also take Poly-fil - which is the same material as polyester quilt batting, just loose fibers instead of a roll - and stuff it into a sump or canister filter. Just use it to replace whatever disposable filter pads you are currently buying, or to supplement your existing media. The important thing to keep in mind with either quilt batting or the loose poly material is that it has to be 100% polyester and not treated with any chemicals in order to safely be used in a filter.

Hack # 3: More Media

So by now you’re seeing that the more media (or surface area) you can get into your filter, the more beneficial bacteria it can support, and the more filtering capacity you’re going to have. A great practice is to cram an extra sponge, a bag of bio-rings, or bio balls into one of your cycled filters if you have unused space. I keep an extra sponge in one of my HOBs, so that I have a cycled sponge on hand if I want to set up another tank (which is inevitable). In the photo below, you can see I have an extra aquaclear sponge stuffed into the empty space on the right side of one of my HOB filters. This space would otherwise be left empty. Instead I’ve increased my filter’s biological capacity.

HOB Filter with quilt batting and extra sponge
HOB Filter with quilt batting and extra sponge

Walking through a pet store looking at the price tags on filter “refills” can be discouraging, but it’s important to note that biological media such as sponges and ceramic rings almost never need to be replaced. Many manufacturers have literature that tells you to discard your bio media after 2-3 months and replace it. This is purely a scheme to increase sales. Ceramic rings and sponges do not go bad, all you have to do is rinse them out in aquarium water to clean them. The only media that needs to be replaced regularly is filter floss and chemical media such as charcoal. In the filter I showed above, the only thing I replace is the polyester batting at a cost of roughly $1 a month. The sponges have been in use for over a year and will last several more.

Hack # 4: Breeder Box Filter

You can take an air driven breeder box and turn it into a customized HOB filter that also acts a quarantine / breeder box. By attaching a sponge to the intake of a breeder box, you’ve already created a sponge filter. You can take this even further by filling the breeder box all the way up with whatever media you want. The great thing about breeder boxes is they increase your total water volume and can hold plants, gravel, bio media, and fish. In my case I use the intake sponge and a bag of biomax rings plus some live plants in the box to add biological filtration while using it for breeding or quarantine.

If you have a large breeder box with vertical dividers, you can create a two or three stage HOB filter that is customized to your needs. You could even use one side as a quarantine and fill the other up with media.

Breeder Box with bio rings
Breeder Box with bio rings

Keep in mind that while all of these hacks will improve your filter’s ability to turn ammonia into nitrate, all those nitrates aren’t going anywhere unless you:

A) Perform regular water changes, or

B) Keep plenty of live plants to soak up those nitrates.


Links to purchase items referenced in this post on Amazon:

Intake Sponges: https://amzn.to/2LqdcLj
Aquaclear Sponges: https://amzn.to/2ur3Gkx
Aquaclear HOB Filters: https://amzn.to/2JphUqJ
Breeder Box: https://amzn.to/2NRMGfb