oxygen for a pleco

Question
hello I have two hypostomus plecostomuses and sometimes one of them floats upside down. I hear that this is normal if they are feeding on food or if they're hungry, but its not if they do this a lot and they are not feeding/ or sucking on something. well, one of mine does do this a lot and I'm wondering what might be wrong with him. He also seems like he does not eat as much as my other one. I think this may be because the other one is aggressive towards him and teritorially.Sometimes he chases him away from the pellets I feed them. I have had both of them together alone for about a year and the more aggressive one seems fine but the other one seems like he doesn't eat as much and floats up side down. Also he will float vertical with his noise in the bubbles from the filter water without sucking on the tank. I'm wonder if maybe he doesn't have enough oxygen. If not how can I get more oxygen in my tank?

Answer
Hi Katie
I just read something the other day on these guys.  And, you're right, they are territorial to each other.  I have 2 in different tanks, and was considering putting them together in my small pond for awhile.  Then read that wasn't a good idea, best kept with 1 to a tank.  I'd give some thought to moving one to another tank if you can, or possibly getting rid of it.  In the meantime, you could try getting 2 veggie clips from the store.  They love cucumbers, zucchini, squash, romaine lettuce-which they should be supplemented with anyway because usually there's not enough algae in the tank for one of them.  Try placing them at separate ends of the tank and see if that helps.  

As far as enough oxygen, you should keep the water line down about an inch or so from the filter output area.  The water agitating the surface is what oxygenates the water by exchanging oxygen and CO2.  If that's going on, and no other fish are showing symptoms, I'd say the one pleco is probably just stressed.  

Hope that helps and good luck!

Christy