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Do you need a pre-filter sponge for your fish tank?

One of the modifications you can make to your hang on back filter, canister filter or sump is by adding a pre-filter sponge to the intake valve. So, is it worth doing?

This guide at Aquarium Blueprints will list out some of the benefits, as well as some potential drawbacks, to using sponge pre-filters.

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What is a sponge pre-filter?

A pre-filter sponge is usually a cylinder like sponge where you can place on the intake of your hang-on-back filter, canister filter or sump. The main purpose of this sponge is to prevent small fish and shrimp from getting sucked into the filter, which will obviously cause several issues.

Do you need a pre-filter?

Whether or not you need a pre-filter depends on the size of fish you want to keep. If the fish is too big to fit into your filter intake, then you most likely don’t need one. If you have smaller fish that might squeeze their way through, however, then it is advisable to get one.

If you are planning to keep nano shrimp, such as the Caridina and Neocaridina, then having a sponge pre-filter is highly recommend. In our experience, the plastic pre-filter that came with our Fluval 306 External Canister weren’t able to keep our red cherry shrimp from being sucked in. Once we replaced the plastic pre-filter with a pre-filter sponge, however, we were able to prevent them from going into our filter.

Furthermore, if you are planning to breed fish, then getting a sponge pre-filter is also recommended. Some species, especially those that are small in size, produce eggs and/or fry that can easily be sucked into your filter if there aren’t enough protection.

Other benefits

There are other benefits to having a sponge-based pre-filter as well. The most obvious of which is that the sponge will provide plenty of surface area for beneficial bacteria to grow. You need these colonies to convert the harmful ammonia and nitrite compounds into the less toxic nitrate. The sponge have little tiny pores, which increase the surfaces exponentially when compared to materials that are completely solid.

Having a pre-filter will also prevent food from getting into your filter. This is great for your fish as they can pick away at the excess food from the sponge. At the same time, they are able to keep the sponge clean, which means you won’t have to clean it often.

Keeping food and other decomposing matter from your filter also means that you don’t have to clean the filter media as often. Instead, you can simply service the pre-filter sponge anytime you notice a reduction in water flow. Keep in mind that having a pre-filter shouldn’t negate having to service your filter as some debris will still get through the pre-filter and end up in your filter.

Pre-Filter Sponge Cons

There are a few cons when it comes to using sponge pre-filters. The first is that, depending on the size of the sponge, they could take up a lot of space in your fish tank. Fortunately, there are smaller sizes available.

The other potential issue that you may run into is that the sponges will clog over time, which will reduce the amount of water from being sucked into and put back out of your filter. If you don’t clean the debris off of your pre-filter, then you could have some water flow issues in your aquarium.

Coarse Sponge vs. Porous Sponge Pre-Filters

When it comes to aquarium pre-filters, there are two types of sponges, coarse and porous.

Coarse sponges are more loose and have bigger pores. Although they may not be as good at trapping food particles and other debris when compared to the other type, they won’t also clog your intake as often.

Porous sponges are more high density and features smaller pores. As a result, this type does a better job at keeping the small stuff from getting into your filter. With that said, porous sponges get clogged up frequently, especially if you have a big bioload. So you have to clean it a lot more when compared to a sponge that is more coarse.

If you want to do less maintenance on the sponge itself, then you should get a coarse sponge pre-filter. If you want to keep food, fish excrement and other debris from getting into your filter (and don’t mind the regular cleanup), then you should get a porous sponge pre-filter.

Measuring the diameter of your filter intake

Before buying a pre-filter, you should first measure the diameter of your intake tubing. You want a firm fit or else the sponge will easily separate away from your intake, which will obviously cause big problems if you don’t catch it on time. It’s fine if the intake hole is a little bit smaller than the intake tubing of your filter as you can easily expand the hole of the sponge to create a snuggly fit.

How to connect the sponge pre-filter

When connecting the sponge pre-filter to the intake tube of your filter, we recommend that you insert the tubing just enough to make it secure. This is because you want to use as much of the sponge as possible. The opening of the tube act as a siphon that will suck up the surround water. If the tubing is halfway down the sponge, for example, not much will get filtered on the top half of it.


We recommend getting a pre-filter sponge if you are planning to breed fish and/or have shrimp. The sponges also provide other benefits such as keeping debris from getting into your filter and offering a lot of surface area for beneficial bacteria.

Coarse sponge pre-filter are better in terms of water flow and require less cleaning. Although porous sponges need more maintenance, they do a better job at keeping stuff out of your filter.

When connecting the sponge prefilter to the intake tubing of your filter, make sure you leave a lot of room so that the water will flow through as much as the sponge as possible while also keeping the pre-filter tightly fit at the same time.