I've never seen an aggressive pleco before o.o Aggressive other fish, yes, but never a pleco... though I suppose it can happen since I've seen surprisingly docile betta...

Though if you haven't had him long then you could always try switching him out for a bristlenose? They don't get near as big as regular pleco's so you wouldn't have to worry about selling him back and could keep him for his entire lifespan Plus if you get a male then they grow that really cool feature on their nose ^-^

 

Yeah, I've seen aggressive plecos. Plecos can actually be very territorial fish, especially when they are not housed in a large enough tank and feel threatened. Giving them plenty of space and places to hide can help. Plecos do go after other fish when they are hungry or stressed out, and can injure and even kill their tankmates. Sometimes, they develop a taste for slime coat and will latch onto their tankmates, which can lead to wounds and infections.

Some species are carnivores as adults and will hunt and eat small fish, so you have to watch out for that too.

 

Like was said, environment often plays a huge role in fish behavior. I think that selling you a pleco was a mistake, expert or not. A nerite snail or two is a much better long term solution to your problem.

 

Make sure your pleco has a hideout that he can claim as his own territory. This ought to help as he will only get aggressive when another fish ventures into his territory or tries to eat his food. Driftwood is a good choice- not sure what type of plec you have, but he might need the wood to rasp on.

My clown pleco head butts my other fish when they get close to the food he's claimed as his. It's really funny to watch, since he's never tried to actually hurt them.

 

I agree with everyone, it definitely depends. Even with proper water conditions and space, every fish has their own personality.
I have a pleco in my tank and he is SO SHY. He does his best to stay out of everyone's way and avoid confrontation. He is a rubber-lip pleco, so he is a bit on the smaller side as plecos go.

 

Some plecos can definitely be aggressive, but they're a bad idea for algae duty - they don't really eat just algae, that's a kind of... last resort, if you will. Snails and otos are far better for algae duty since they'll go for it if they find it. Plecos will eat vegetation like plants and actual veggies, but not algae.

 

What species did you get? Most petshops sell common plecos which get HUGE, like over a foot huge. However there are some species that are supposed to be great at it - bristlenose plecos, I think are one of the species and they stay about 4 inches.

I have 2 clown plecos but they dont really eat algae - they eat wood or something on the wood and veggies and they max out at 3 or so inches. I seldom see them but I dont think they are agressive to each other

Check this out for info on different algae eating pleco species

http://plecoplanet.com/?page_id=615