Welcome to the site!
I would think twice about taking much more advice from them. It sounds like they were just trying to make money off of you.
You have poor fish in toxic water. PWCs may be in order. Ammonia can/will burn the gills of the fish. A complete cycle would be indicated by 0 ammonia, 0 nitrItes and some nitrAtes.
What you are now seeing are called diatoms. They will burn themselves out and there is no need to add any chemicals to your still cycling tank.
I would suggest you get your own test kits. This will help you learn how to test and learn the way your tank works.
We are here to give free advice based on our personal knowledge and experiences. Your LFS
needs you to buy their stuff to keep them in business. They want your money.
We want your pics!