Depends on your P's. Of course, if you can get one at least the size of your P's its got a better shot at making it. Though plecos are pretty tough. I've had a 3-4" in w/ two 4-5" RBP's in a 29 for 4 months. Reds outgrowing it. Just keep the reds well fed when you introduce.
I really know aggressivness depends on the fish itself and not the species, but i've noticed that my caribe, and piraya absolutely hate plecos and constantly kill em. But while the plecos where in the tank with only reds never had a problem.
i have a 12'' common pleco with my 6p's for a few months so far so good but he only comes out at night he is safe because he has a hiding spot i would suggest you rig up a little cave for him to crash during the daytime if he is out of site it wont bother your p's as much good luck
i have found with plecos adding them when p's are small is better ,i added a 4'' pleco with 1'' reds and he is still alive after 1 1/2 years.
i only sold the 2 8'' reds last week keeping 2 5'' + reds and a 4'' piraya the pleco is @ 11-12'' and only gets problems of the piraya .
add a much bigger pleco to have a good chance .
i once added a 5'' pleco with my other reds 6'' @ 2 1/2 years ago and it was gone within a few hours but they were very aggresive but i sold them
I have a 6" sailfin pleco, a 4" common pleco and a 2" clown pleco in my redbelly tank. The first two are with my piranha's for almost a year, the clown pleco just two months... Only the big one gets nipped occasionally, but, amazingly, its fins are usually healed the next day, even if they were pretty torn up.....
I would say pleco's are the safest fish to keep with piranha's (perhaps besides raphael cats), but you will never know how old it will get: it might be killed within a day, or after living with your piranha's for years.....
I had a 4" Plecos with my old 5" RBs before. They'll be fine if you have enough cover for the Pleco to hide or stay away from until night time when they usually do most of their scavenging. Its your call on getting bigger ones, to me, its more a hassle since the bigger ones sh*t bigger spagetti strings which looks like swimming worms when caught in the waterflow of your tank.
The only plec and catfish that i could keep alive. Were with reds. As soon as i had gotten cariba's and piraya Bam lunch The first cariba casualty of many
And i had this guy for over two years with reds.
i have a 7.5" sailfin pleco in with just my neon tetras, and other livebearers in the 33. He's moving to a 150 gal, in 2 weeks. He should be happy. He's been stuck in that 33 for 8 months now. I hope he gets massive.