Santa Monica Filtration DROP1.2X (tm) Drop-in Upflow Algae Scrubber ATS Aquarium Filter Turf Saltwater Replaces Chaeto Reactor Protein Skimmer Sponge Canister Pellets Zeo Waterchange Probiotics 4 LEDs, for saltwater up to 0.5 ppm phosphate, and freshwater even higher Adds oxygen, pods, and raises pH of your aquarium water Can't overflow onto your floor, because it is always under water Removes ammonia, nitrite, nitrate, phosphate, nuisance algae, CO2 from your aquarium water Special plate on bottom blocks red light from coming out, and lets you sit the unit on the sand below