Any sized tank can be as planted as you like. :) Some people plant tanks so tiny that a shrimp can't even fit. Search for nano-tanks for inspiration.
I would use at least the following plants:
- java fern (attractive, very low-maintenance. Just tie it to something - don't bury the roots - and watch it grow).
- anubias (ditto. Nice flat leaves make great betta-beds).
- java moss (even lower-maintenance and very versatile. You can make a wall, a carpet, tie it to decor or rocks, or just let it drift around the substrate).
- hornwort (root it in the substrate. Grows very easily, and you can trim it every few days/once a week to keep it a sensible size).
- elodea (ditto).
- wisteria (ditto.
- lacefern (ditto, though it can overwhelm a small tank very easily).
- ludwigia repens (ditto. This plant turns a beautiful red under higher light. I dosed mine with a bit of Flourish Iron to maintain the colour).
A bit of driftwood or some rocks for a hardscape can act as a nice centrepiece or add structure to a planted tank. :)
Re the heater: you probably don't need it for warmth, but I'd have one for stability anyway. If you get a sudden colder front, a heater will stop things changing too rapidly. It's especially important in a smaller tank as they don't hold temperatures nearly as well as larger ones. If you had a twenty gallon, I'd say not to bother, but with a 2.5, I'd be on the safe side and have one just in case. You can never be too prepared!
Last edited by Bombalurina; 11-13-2013 at 04:02 PM.