Why You Need a Pre-Filter Sponge for Your Aquariums

Looking for a very easy way to optimize your hang-on-back (HOB) or canister filter? Try a pre filter sponge (or intake sponge). This simple foam cylinder has a hole in the middle that allows you to slip it onto the intake tube of your filter, much like a sock. But why in the world do we need a prefilter sponge when we already have an aquarium filter? Intake sponges have a surprising number of benefits, such as:

• They provide more surface area to grow beneficial bacteria, which purify the waste chemicals in the water and make it safe for your fish to live in.
• The filter intake tube often has large openings that allow sizable objects to get sucked up by the filter, potentially ruining the motor. The pre-filter sponge prevents things like baby fish, dwarf shrimp, little snails, plant leaves, and fish food from entering the filter.
• An intake sponge adds more mechanical filtration, thus keeping your filter media from getting dirty as quickly. This is important because dirty filter media does not function as efficiently, and we would much rather clean an easy-to-remove intake sponge than the filter media buried deep inside a canister filter.

Prefilter sponge installed at the end of a filter intake tube

Which Pre Filter Sponge Should I Get?

Our sponges come in three sizes — mini, medium, and large — and we purposely designed them with coarse foam that has larger porosity. This means that our pre-filter sponges do not remove super fine particles, but they block out most other particle sizes and won’t get clogged up as quickly. Our mini pre-filter sponge is best for smaller fish tanks and filters with slow flow, whereas the large pre-filter sponge is well-suited for bigger aquariums and filters with fast flow. To help you select the right size, see our chart that lists some of the most popular filters in the fishkeeping hobby:

A pre-filter sponge can also be used with our power head to transform it into a mini power filter. Just attach two zip ties to the powerhead's intake basket, cut off the excess tails, and slide on a large prefilter sponge.

How to Install a Pre-Filter Sponge

1. If the filter’s intake tube has a large basket that is much wider than the tube, then remove the basket.
2. Slide the prefilter sponge partially onto the intake tube so that it is just covering the tip of the tube. The sponge should be positioned at the very end of the intake tube so that water travels more evenly through the entire sponge and the foam does not get clogged up as quickly.

O-ring attached on the end of an intake tube to keep the intake sponge from slipping

3. If the sponge is too large for the intake, use one of the following methods to make a tighter fit:

• Get an O-ring kit that contains many different sizes of O-rings. Find an O-ring that snugly fits on the intake tube, and position it about 1–2 inches (2.5–5 cm) from the end of the intake tube. Slide the pre-filter sponge over the O-ring on the tube, and the sponge should stay put.
• Get a plastic zip tie and tighten it around the end of the intake tube, about 1–2 inches (2.5–5 cm) from the opening. Cut off the excess tail so that the buckle is still attached. Slide the sponge onto zip tie on the intake tube for a very firm fit.
• Cut off a small rectangle of coarse sponge pad and slip it inside the intake sponge. Slide the intake sponge onto the tube, and make sure it fits securely.

Zip tie attached on the end of an intake tube to keep the intake sponge from slipping

If the intake tube has an odd shape, you can still make your own DIY prefilter sponge. Buy a coarse sponge pad and cut off a section of sponge to a) stuff inside the intake basket or b) wrap around the entire intake and attach using zip ties.

To see a video demonstration of how to install and properly fit a prefilter sponge, watch our tutorial here.

How to Clean a Pre Filter Sponge

The intake sponge is essentially like a trash can that collects fish waste, old food, and other debris in the water. Once a month or whenever you see the water output of the filter has decreased, make sure to “empty the trash” and clean your pre-filter sponge.

1. Use a plastic bag to scoop the sponge out of the water so that the detritus won’t spread and make a big mess in the aquarium.
2. Squeeze and wring out the sponge several times in old tank water inside the plastic bag.
3. The dirty water is like a mild fertilizer for plants, so pour the dirty water onto a houseplant or the lawn if possible.
4. Repeat Steps 2 and 3 multiple times until the water inside the bag is not very dirty.
5. Place the pre-filter sponge back onto the intake tube.
6. If there are lots of particles floating in the water, just wait an hour or so for the filter to clean it up again.

Adding an intake sponge to your filter is an easy way to upgrade your mechanical and biological filtration, while protecting your baby fish and invertebrates from getting sucked up. If you are not sure which aquarium filter to use, make sure to read our filtration guide for beginners.