Unfortunately mondo grass isn't a true aquatic plant. Sadly it will die and rot in your tank eventually. Is there any way you can return it? The red ludwigia is also a very finicky plant, they don't keep their red coloration well at all unless you fertilize them, particularly with iron, and give them lots of fluorescent light. Personally, I would return these plants and get something easier to care for, like anubias, java fern, and java moss. You're definitely off to a good start, though. Have you considered getting him a heater yet?
I use and recommend these: http://www.fosterandsmithaquatics.co...m?pcatid=11368