that pleco can grow pretty big(around 12" I believe), but a 120 should be fine for it. Frostyone is right, check out planetcatfish.com. I have sand in with 2 plecos. One of them being a royal pleco, the poop king of the pleco world. you will have to experiment a bit but with proper filtration and water movement(i.e. powerhead) you can keep the waste to a minimum. I have two ac110 that create a rolling effect with the water that pushes the waste to the back wall of the aquarium where the uptubes for the filters are. I plan on adding a powerhead on the side shooting across the back wall to help push the waste into one corner. I plan on putting gravel in that corner for the waste to get trapped, then in theory I should only have to siphon the one corner. Overall I am pleased with my sand with my plecos just have good current with no dead spots.