The first week of December '07 I received two (one orange/blue, one blue/green , approx 1/2") ricordea in a package from Drs F&S. I've been feeding and they're presently about 2". How large can I expect them to get? How quickly do they spread without assistance? The rock they're on is about 12" x 12". Do I have room to add a couple more (thinking of different colors) or do I need to leave well enough alone?