When I first started the 46ga bow last Feb I used Purple-Up. Cant say it did anything harmful, but cant really say it did anything good either. I would say, get a nice piece of rock w/ lots of coralline and seed it that way. Oh and check your calcium levels on a regular basis. Good luck!!!
Save your money. Get your Cal, Alk and Mag levels up to the correct levels and Coralline will start to grow in the tank. If possible try and get some scraping from someone to seed the tank.