I started off with two of them in a 10, and as they grew ended up with the 2 in a 30. Unfortunatly 1 grew larger than the other and picked on the smaller one until it passed. I kept her alone for about 6 months until I managed to find another columbian her size, which went good for about 6 months until she again picked on the smaller one until it too passed. I have since just put a common pleco in the tank which stays out of her way.
My problem is that she has ALWAYS basically swam in one spot. In the small tanks it was by a biological bubbler in the corner. She just swim's 24/7 in the same spot except when she's eating (which my avatar... that's her). Now since I've taken that bubbler out she swims 24/7 at the output of the HOB filter. It's like she's always trying to swim against a current. I put a small pump from a water fountain in there before to create a good current, but she still never moved from the spot (again, except for when she's eating).
I have never been able to figure it out. I do know that she needs a bigger tank, but I am a college student and have to move the tank 4 times per year between school and home, so a bigger tank isn't an option. She still has PLENTY of room to swim around, but still I know she needs bigger. I graduate this year and will be moving somewhere for good. I actually already have the 55g that I'll be putting her in (and will later upgrade to a 100g). It's just a waste of time for me to set it up right now.
Anyways, I've had her for over 3 years and she has been nothing but healthy. It's nothing wrong with my water params as the tank is stable and I've never had any problems. This is something she has always done since a few months after getting her.
-brent
Edit: She is 6.5" right now. How long have you had yours?
