i have a 125 gal with one arowana and 2 oscars and a bichir and a plain old pleco. he's about 8 inches and the biggest thing in the tank. they are all juveniles. the arowana is about 7 inches and the bichir is about 6. the 2 oscars are 3 & 4 inches. my point is that i think one big pleco is enough for a 125 gal. they also generate a lot of waste.