Greg Watson makes dry ferts. A carpet plant, meaning... a ground cover? That will depend on what type of ground cover plant you want. Some ground cover plants will do fine with PC, some need stronger lights.
Yes, a ground cover plant. I looked up some, and decided that I like hemianthus callitrichoides, dwarf hair grass and Sagittaria subulata, but I really like the first one.
For the h. callitrichoides you are going to want co2, and really strong lights, otherwise it will grow very slowly (without co2), or will grow very tall (weak lights).