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The Design Elements of the Best Aquarium Sponge Filters for Your Fish Tank

Updated on May 4, 2010

The Best Sponge Filters

DIY options are plentiful when it comes to sponge filters. Some are more successful than others. There are several design elements that can and should be incorporated into any DIY sponge filter. The low purchase price of manufactured aquarium sponge filters means that the only reason anyone would go through the trouble of making their own sponge filter is to make one better! Better yet, make one the best!

If you're unfamiliar with sponge filters, you may want to start with my article What is a Sponge Filter, How It Works, and Why Choose One. If you have no interest in making a sponge filter, you may still want to read this so that you will know what to look for in buying one. Then you can hop over to my Buying The Best Sponge Filter hub to narrow down which particular one you want.

Whisper Air Pump and Some Powerhead Choices

Rena Air 200 Air Pump
Rena Air 200 Air Pump
30 Gallon, quietest, most reliable air pump. Click to find other sizes.

Air Pump or Powerhead?

The first thing to consider is whether to power your sponge filter with an air pump or a powerhead. In larger tanks a powerhead may be necessary to achieve an effective range. For any tank less than 35 gallons, it's probably best to stick with air power.

Air power is gentler, first of all, but when the sponge filter is properly made the flow power created by it can still be quite strong and far-reaching. Meanwhile, the thrust of a powerhead can draw debris deep into the sponge, often leading to clogs in the sponge and difficulty in cleaning them. This problem would affect smaller pored sponges more often, but larger pored sponges have their own problems with powerheads. Again, the powerful thrust can quickly wear paths of least resistance through a larger pored sponge. Either way will greatly reduce the effectiveness of the filtration, and wear the sponges out more quickly.

Still, sometimes a powerhead is preferred, such as in the case of a larger tank. The trick then will be to set the powerhead (adjustable preferred) at just the necessary speed to achieve the filtration range desired and no higher, and to use sponges with pores neither too fine or too large.

It's always possible to set up two sponge filters in larger tanks, to avoid using powerheads and losing the gentle air-driven flow. One can be set up on both sides of the aquarium to increase the suction range. If the tank is long enough, additional sponge filters can be set in between the end ones to avoid dead spots.

Choosing a Sponge for Your Filter

An efficient sponge filter will include an efficient sponge. It should be long-lasting, highly porous, and the pores need be of the right size for your needs. Generally larger pored sponges are best, giving plenty of surface area for the growth of beneficial bacteria, and providing for better flow. But of course, larger pored sponges let a lot slip by, such as fine particles, and fish.

Sponge Filter Parts

Replacement Sponge F/A900-902
Replacement Sponge F/A900-902
Fine-pored for fry tanks.

Shocking I know, but if you use small pored sponges to protect the little fish fry, then the more likely it is that the sponge will become clogged, lose flow and need more frequent cleanings. However, in breeding tanks or grow-out tanks where small fry are being raised, the pores need be small enough to prevent the fry from being sucked through the sponge filter.

The sponge's pores -in short- need to be large enough to avoid clogs, but small enough to catch fine particles, big enough to promote a strong flow, but dense enough to avoid the bypass effect of paths of least resistance.

Uplift Tube Specifications

The uplift tube plays a huge part in the sponge filter's success, or lack there-of. Several conditions must be met by the uplift tube, but often aren't. Of course, first off, it should be made of hard, rigid plastic, wide enough to insert your airstone, plus a bit for optimal water flow, and it should be long enough to extend from its position within the sponge up to within 3/4" and 2", giving room for expected evaporation. This piece can be cut down to size with a hacksaw once fitted.

Next, the tube needs to be inserted well into the sponge, in order to allow for maximum draw through the sponge material. The tube also needs to be perforated at that end which the sponge will cover. If the sponge does not wrap around the very bottom of the sponge, then the bottom of the tube needs to be sealed with an end cap.

This is really the only way to make a sponge filter. If you don't have these two elements, the whole concept fails.

The water needs to draw through the sponge from every direction. If the base of the airlift tube -the base of the vacuum and suction- is resting too close to the top of the sponge, it will only draw water through the top of the sponge.

Conversely, if the tube is fitted deeper into the sponge, but not perforated throughout that section of the tube which will be covered by the sponge, then it is not drawing any water from the top of the sponge at all. However, if the airlift tube is also vented or perforated above the sponge, then the vacuum effect in the airlift tube is dispersed and broken. So using your girlfriend's hair curler will not work.

Not only must the airlift or uplift tube begin deeply enough within the sponge, it must extend upwards far enough above the sponge to provide a sufficient vacuum effect. The length of the uplift tube establishes the strength of the flow, and the range of the suction. If the water is spilling out of the tube mere inches above the sponge, then there is no strength in the flow, and the exiting, filtered water will merely drop back down to the sponge to be sucked in an filtered again and again. The higher the uplift, the stronger the flow, and the wider the exiting water is disbursed. Both the wider disbursement and the stronger flow contribute to giving the sponge filter a greater range of suction.

Uplift tubes should extend to just below the water's surface, allowing for normal evaporation. This provides for maximized vacuum effect and more surface disturbance, essential especially if the sponge filter is the sole source of air to the tank.

The vacuum effect created by the taller uplift tube is as responsible for tank-wide flow and suction range as the 360 degree suction through the sponge is responsible for the sponge filter's superior biological filtration. No matter how well the sponge is filtering, if it is only refiltering the same water over and over, then it's not doing a very great job. So a proper uplift tube of the proper height for your tank really is quite necessary.

I like to use Lee's Aquarium Undergravel Uplift Tubes (available above). The kit comes with an angled water return piece, with the main tube in varying sizes as much as 12 inches tall. These uplift tubes can be drilled to produce the venting at the sponge end, or holes can generally be punched through with a hammer and a nail, if you're careful. The taller tubes allow for greater tank-wide circulation in most tanks, and can be cut down to smaller sizes if necessary with a hacksaw. A four inch connector piece is also provided in the kit.

Making Better Best

A sponge filter that can disburse the filtered water at an angle just under the water surface creates an even greater tankwide flow. The water movement away from the sponge filter at the surface level will lead to water flowing towards the sponge filter along the floor of the tank, at the sponge intake level.

For this purpose, powerheads do excel. However, in a smaller tank the effect can be copied by air driven pumps with elbows at the top of the uplift tubes, or by an adjustable tube which can be tilted, or is simply built with the tube at an angle. This angled return of the water creates the desired flow, providing there is adequate vacuum.

This desired tank-wide flow increases the filter's range and effectiveness, and also promotes healthier gas exchange at the surface of the water, providing the tube exits close enough to the surface to allow for exchange. So you see, all the elements tie together.

Sponge Bottoms and Wall Mounted Sponge Filters

Keep in mind as well that a tiny amount of space left between the bottom of the sponge and the bottom of the tank or top of the tank substrate will help the sponge filter to draw water -and debris- from the bottom of the tank. Ideally, the sponge on a sponge filter will draw water from all around it, 360 degrees, excluding only the direction of the uplift tube. Sponges that sit directly on the bottom or on huge obtrusive bases are leaving a large amount of dead space. Anything trapped beneath the bottom of the filter, stays there.

With this in mind, sponge filters which attach to the wall of a tank via suction cups can still be quite good, provided that the bottom of the sponge is located as closely to the floor of the tank as possible without actually resting on the substrate. With an angled uplift tube, it'd be even better.

Good Manufactured Options

Fluval Edge PreFilter Sponge
Fluval Edge PreFilter Sponge
Just fit over the intake tube of your power filter or attach to power head leading to canister filter.

Final Tips, Use and Maintenance

Final Tips: The quietest sponge filter will utilize an airstone. The finer bubbles will cause less friction on the surface. Using a powerhead instead of an airpump to drive the suction in your sponge filter will give it greater range for larger tanks. It's better to have some weight in the completed unit if it is not placed with suction cups so that it will be abe to hold its own position in the water. To cut sponges into desired shapes, or holes into desired sponges, it may be helpful to soak the sponge and then freeze it, providing for a crisper, cleaner cut.

The features advocated in this article make for a highly effective sponge filter, optimizing the concept to its greatest potential. Whether making a sponge filter yourself or buying one, these features should be kept in mind.

When your Sponge Filter is all set up -whether a purchased unit or a DIY- and the airpump or powerhead is connected, just squeeze the sponge to release all the air and buoyancy, position within the tank while squeezed, and plug in the power.

Turn off and remove the sponge every week or so -as your bioload requires, but at least once a month- to rinse it out in removed tank water. Rinse and squeeze out until all debris and discolored water is removed.

Replace sponge onto filter keeping it squeezed to release air and return power supply. Sponge filters are self starting.

Replace sponge with new one whenever needed (6 months to years). It's really such a simple, easy to use and maintain, inexpensive solution that there's no reason not to utilize one.


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    • profile image

      Ahmed Bello 

      9 years ago

      This made an excellent reading. I will be practicalizing immediately. It has given me a good understanding of the whole concept and i am really grateful.

      It is comprehensive!



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