They are know as rapid sand filters. They have been used on very large aquariums, usually public aquariums for many years. Yes, they are very similar to swimming pool filters. In this application they are primarily mechanical filtration devices.
They are actually quite simple. A sandbed, sometimes with different side material, is used to filter the water. Usually the water flows from top to bottom, through course to fine material. To clean the filter, you use a series of valves to run the water in reverse. This lifts out the accumulated dirt. The process is know as "back flushing". The water used to back flush the system is not normally the tank water, and the dirty water is discarded.
The big advantage is a filter that is easily cleaned.
Obviously there is no biological filtration in a system like this, so other means are used. For some public aquariums, that are using an open system the resupply of new water is no problem, so biological filtration isn't needed. (Note-open systems are systems that have a direct connection to the ocean or other salt water source.)
If you want more information on these filters, you can obtain a copy of Fish and Invertebrate Culture: Water Management in Closed Systems by Stephen Spotte. Warning, this is a very old book, and the information provided in it is considered "pre-reef aquarium" knowledge. Do not use the information in the book with out confirming it in newer state of the art books.
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