First, welcome to Tropical Fish Keeping forum. And to this hobby.
Second, I moved your post out of the thread in which you posted it and started its own thread. More members will see it here, and you'll get a better response. If you click the blue button "Add New Post" while in a thread, it will post in that thread. To start a new thread, go to the list of threads in the relevant section of the forum and click the blue "New Thread" button.
Now to your question. Can you give us the water parameters? GH (general hardness) and pH is what we need. The GH you can ascertain from the water supply people, they probably have a website. They may be able to tell you the pH too, if you don't have a pH test kit.
Also, how long has this tank been running? How did you cycle it? Are there live plants? What is the temperature?
Lots of questions, and likely more will follow, but we can't diagnose problems without the data.