I think you got started on the wrong foot, The undergravel filter was my first clue
The second was that you added bacteria to a tank that already had fish in it.
It's not exactly starting over but before you buy anything else I think you should read
THIS
I'm not sure who gave you the information to get started but my guess is the LFS. Most LFS give crappy advice or just plain bad advice.
Spend the extra money on quality equipment and test kits or you'll end up buying them later and spending even more money.
Ditch the UGF and Crushed coral if your using it and put in a sandbed and invest in a good skimmer.