Hi Aqui.Water gardening direct is another,for everything to do with ponds.i use them all the time.
Two years ago my pond was nearly over run with parrots feather.I cut it back so hard that last year it gave up the ghost.This year i bought one pot,split the contents into 2 and it is thriving again.The same has happened with the elodea.The best one is hornwort,but again can get out of control if not careful!! :D