Posted: Sun Dec 06, 2009 3:16 pm
For sure skip the 55, and maybe even the 75. A standard 75 gallon tank has a 48"x18" foot print. A 90 gallon has the same footprint, but is taller.
Since you have a female, you're going to eventually need at very minimum a 75, and anything bigger is better. Now, depending on how big she is, and how big she's going to get, a standard 75 or 90 might not work for width. My female is in a 90, and she's only 8.5". She has enough room to turn around comfortably, but if she were any bigger, it'd be a tight fit.
That's why my *favourite* tank is a 4'x2'x2' 120 gallon. It is a standard size, though I find here they are in demand. It's nice because it still fits in a 4' space (the next size up is usually a 6' tank), but it's also nice and wide for turtle.
As for getting a second turtle, don't do it. Your older, established female will view the new turtle as an intruder, and fight with it. If the new turtle is smaller, then your gal could end up killing it. Even if they did get along, you'd need a 200 gal+ tank.
First work on upgrading your current RES's tank, and then, once she's all settled, if you still want to get another turtle, consider setting up a second tank.
Ralpheal, "The 'L' is silent."
Frankie, "Young at heart."