How much b-ionic or two part you go through depends upon your existing levels and the demand of your system. A cup a day on a 55 sounds like a lot to me.
I switched from b-ionic to Randy's recipe not all that long ago (I use recipe number one) and I'm very happy that I did. Why buy when you can make your own? I can keep up with trace elements through water changes. Also, the reef chemistry calculator is just the greatest thing, you really have to use it. Enter your water volume, your existing levels, your desired levels and the product your are dosing...and viola. It will tell you how much you need to add. It will also tell you your approximate rate of consumption base on the above and what type of demand you have.
Here's the link:
http://home.comcast.net/~jdieck1/chem_calc3.html
Click on traditional and you're on your way.