Sponges can typical pump water equal to 4-5 times its own volume every minute. For a sponge about the size of a football, this equates to several thousand liters each day.
The original and one of the largest list of DIY reef aquarium project links you will find in one place. The large list of links is almost been totally added into the new format, with the number currently (12/01/2006) being 483.
If you have a link to suggest, then please submit it for consideration. Or if you find one that has expired, then please
me so that it can be fixed. You can also let me know what you think of the new format and if there are any improvements that can be made to the way the information is presented.
Detailed instructions, diagrams and photographs of a controller to be used with an RO filter. Water levels are detected using float switches in the RO reservoir and saltwater reservoir (used for water changes). Depending on the state of these, the unit switches on/off solenoid valves to fill the reservoirs to desired levels.
Details and sample calculations showing how to determine the load a floor can handle, and hence whether it will be able to support your aquarium. In French.
DIY Links 
General websites that have a number of DIY projects listed on them. The individual projects will already be linked in the sub-catagories.
General electronic projects that don't fall into the other catagories here. Including a pH probe and water level alarm.
Recipes for food for fish, corals and other organisms within the aquarium system.
General equipment required for a reef aquarium, covering things such as tanks, stands, plumbing etc.