Zuska -
I couldn't help but notice you were going to purchase a yellow tang in the your closed "group buy" thread. I assume that is NOT going to go in a 6 gallon nano, no matter how small it is when you bought it. You need to take care of the issues you have with the tank you've got before you go adding more fish and other livestock to it! Also, you're going to buy a crocea clam? You don't have the lights to keep one! And once you do, it's often much better to start with the less demanding T. derasa.
Secondly, you can't seem to manage the tank you already have. You've lost a lot of fish, you're using tap water, you need more live rock, a better skimmer and you don't even know what a quarantine tank is... and you want to set up a 6 gallon nano? That is going to be ten times as difficult as the larger tank you already have. It will require better husbandry, more water changes, more careful monitoring and MORE KNOWLEDGE than you have demonstrated your current capacity for.
I am normally not harsh in my comments in beginner threads because I feel like people are trying to fix problems and trying to learn. I am usually very patient. But this is ridiculous, and if no one else is going to say it, I certainly will.