about fish tank

Question
I have gold fish,Angel fish and black shark but i want to add another fish which fish i have to add please suggest me?

Answer
Hi Suraj,
Goldfish, Angel fish and Black shark are not  fish that you can put together in a tank.  The reason is that goldfish like cool water  alkaline water, Angel Fish live in warmer acidic water, and the black shark is an aggressive fish.  Keeping these fish together in a tank will result in disease and death.
If you write back to me, and give me the size of your tank, I could tell you what fish you can put in that are compatible.  I would also want to know a few more details.  What is your PH? and water chemistry?  Please give me all the information you can on your tank, and what kind of fish you like.
Lynda