I hate to be the bearer of bad news...but you should probably take all of your fish back to the store. What you are going through right now, I'm assuming is an ammonia spike. Is what's floating at the top of your tank kind of milky stringy looking gunk?
See, tanks are not meant to be set up and then have fish put in immeadiately. It takes time to establish a healthy supply of good nitrifying bacteria in your filter media. All fish waste contains ammonia which is a poison. This bacteria helps to break down the ammonia into less toxic compounds. However there is no or very little bacteria in a newly established tank. There are many pinned articles on how to properly cycle your tanks in order to establish this bacteria. Generally it takes close to a month. I suggest you read this article. And for the sake of your fish you shouldprobably bring them back to wherever you bought them from. And if you intend on serious fish keeping in the future you should defitenly invest in a water test kit. (freshwater).
You should also probably give a good read on every article contained in this link.
Beginner startup articles
Good luck. You have quite the journey ahead of you.