It sounds like you need to learn about your water. Have you read about cycling your filter and have you learned what BB (beneficial bacteria) are?
There is a link in my signature to start otherwise go to the articles section in the top bar of the website and start reading through the articles for getting started and Fish-In Cycling by Jetajockey since you already have fish.
I would start doing some research about the compatibility of fish and invertebrates.
You can to a good place to start learning more about keeping fish and Inverts safely.
Please go to the appropriate sub forum to ask questions so that people will be able to see them specifically and answer better for you.