I have a Fluval Ebi 7.9 gallon CRS tank. The CRS have been in the tank since May 2011, so they're older and I actually only have 7 left. I would like to add some more CRS if I can find some to order. I have read that a lot of people use sponge filters in their shrimp tanks. I would like to add a sponge filter as an additional filter. Last year I replaced the Ebi stock internal filter with a Zoo Med 501 canister with a sponge over the intake. I've always used canister filters or HOBs, but I've never used a sponge filter. I'm not sure how they work. What exactly do I need to buy to add a sponge filter to my shrimp tank? What's the best sponge filter to buy? What is the best air pump? Do I need anything else other than airline tubing?