Welcome. A fish forum is a great place to learn.
Your problem may or may not be created by the Top Fin Water conditioner. There is really not enough information in your post to help you here, but if you're willing to answer several questions, the we'll see what we can do....
Did you cycle the aquarium before adding fish? (If the answer is no, or, what does that mean? and your aquarium is fairly new, then that's you're problem right there.)
How many fish? and what types?
Is the water the right temerature for the species being kept? And are the species compatible?
What filter are you using? What's you're water change routine?
What are you're test results? (Assuming you have test kits... (you need, at the minimum, tests for ammonia, nitrite and nitrate.)
You're post was too brief for me to get an idea of you're experience level, but I do get the impression that you are an absolute beginner. (Which is just fine, the people on here can help a LOT!)
Let me know the answers to these questions, and we'll go from there!
Happy fishkeeping.
