I don't agree with those people who told you that Ray. Yes, the system is sensitive, but not so much that things will change in a matter of hours.. maybe a few days to a week.... but that also depends on your fishkeeping habits... whether or not you overstock your tank (which you shouldn't anyways), and how much you feed your fishes (do you overfeed? lots of leftover food floating around?). I've been keeping my planted 10g for almost 1 year now, and there have been no casualties except when I've had no power for 3 days, and the water temp dropped dramatically.
if it was a salesperson who told you this, then they were just trying to make a sale.
Arcab: why don't you try Hemianthus micranthemoides? It has small leaves, grows nice and bushy, and easily trimmed.
BTW: what are your tank specs? maybe I can be more helpful once I know what kind of lighting and now much of it you've got in there.