Most aquarium filters now use a motor to force water through some kind of filter pad which must be replaced at intervals. However, before there were reliably sealed electric motors, most home aquariums moved water using the "airlift" principle, in which a rising column of bubbles pulled water through the filtering material. This is an elegant and just about failsafe method. Debris in the tank cannot ever jam the external air pump which feeds the filter, and if electricity is interrupted, the filter cannot lose siphon, it simply starts bubbling again when power is restored to the air pump. Many fish love to play in the rising stream of bubbles.
Hydro Sponge filters, first marketed in the 1990's, are a more recent application of the airlift. Hydro Sponge II is intended for aquariums up to 20 gallons. Made of dense, strong plastic with a weighted base which holds the sponge up away from the aquarium bottom, they dismantle easily for cleaning of the sponge. The pores within the sponge provides an enormous surface area for colonization by beneficial bacteria providing very thorough biological filtration. They can be powered by an air pump with or without an airstone (using an airstone will give finer bubbles and make less noise), or with an electric powerhead for those with larger tanks or who simply feel the need for more energetic water movement.
It is difficult to imagine such a simple device working well. Surprisingly, they are excellent, and can be used as the only filter in the tank for many applications. I've used them on tanks sized from 10 gallons up to 75 gallons, always with good results. The local fish store where I shop has an expensive trickle filter for their dozens of tanks, and every single freshwater tank also has a Hyrdo Sponge or similar sponge filter as well. Apparantly the sponge is doing something which the trickle filter doesn't?
Maintainence is as simple as the filter. When you perform your periodic aquarium water change, (20% every week) save some of the old water in a bucket. Separate the top and bottom parts of the filter and remove the sponge from the tank. Squeeze it out in the bucket. See all the stuff which the sponge removed from the water? Reinstall the sponge and refill your tank. Go have dinner with the money you saved not purchasing replacement filter cartridges.
In sum, a clever and elegantly simple device which works very well.
I cannot understand why this product is so difficult to find in local big-box pet supply stores, except that it keeps you from returning to purchase replacement filters on a monthly basis, which incidentally can become quite expensive over time. A great money saving filter that works better than more expensive "power-filter" units you can buy off the shelf.
If you do a little online research you may find that the combination of this type of filter with a "power head" aerator will not only keep your aquarium cleaner and help your fish stay healthier, but it will also save you time and money as a result of its simple design. By merely rinsing the filter periodically, you will keep your aquarium cleaner without all the hassles of draining your aquarium regularly or buying replacement charcoal filter bags as is the case with popular "power filters" found in most big-box stores.
I have a small 10 gallon tank that I retrofitted with some 1 1/4" hose to make the Hydro II sponge filter (20 gal) fit properly. I should have bought the 10 gallon version that is not quite as tall. Now my tank stays cleaner, longer, and I am pleased not to have to drain my aquarium every ten days because of "power-filter" clogs or failure.
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I have this hooked up as a prefilter to a bio wheel 100 HOB on a 10g FW tank that I'm cycling. It's great because I've noticed even thought the water was clear when i put it in it's not full of food that my cycling minnows can feed off of. There is lil to no flow restriction. I hope is stays that way. May change after time and buildup of bacteria and waste/food particles. Best part is that it's wash and go and saves my HOB's filter from getting clogged due to the sponges huge surface area.
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I use these on my fry and grow out tanks. They work excellent and highly recommend them. I use the airstone inside for quieter operation.
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I use this sponge filter as a secondary filter for my 10G hospital/breeding tank. I use it with a Hagen AquaClear Power Filter Mini 20 (100) The Aquaclear is turned off from time to time(new fry) but the sponge filter is constantly on. I use the sponge filter with and airstone and I have no problems. Now, I can't speak on how this operates as an "only filter" but for secondary needs it's great.
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I needed new powerheads after getting a wavemaker since my existing ones rattled and groaned more and more every time they restarted.
