i have 7 (3"-4") rbps with a 7" pleco in my 120g. as someone said earlier i made sure that i bought and introduced my pleco to the tank first and then added the then < 1" rbps aswell. as of right now the pleco seems to be rather dominant/aggressive around the rbps and gets right in with then when food it presented. he has no bite marks on his body and the only fin with any bites taken from it is the tail, and those are very minimal. i have found that up to this point they can cohabitate as long as they are not competing for food or hiding spaces, as both tend to like darker areas. i hope this peace will continue but i really dont know what to expect, the p's really respect him now but + 5" from now and it may be a different story. this is just my experience tho, good luck with your setup!