The hard part about transplanting cat tails is digging/harvesting the plants. You'll need waders, a spade, shovel, and some buckets or wet gunny sacks to put them in. They grow easy once you put them where you want them to grow.
Duck weed is easy too and grows very fast...like a weed.
Simply get a large fish net from a pet shop or walmart and get some. Put it in gallon zip lock bags. A gallon of duck weed is a lot.
Dump it in your water and it'll take off, grow very quickly.
The problem is pond fish eat the heck out of it. I can't keep it in my fish pond for long.