Black fin shark (catfish)

Question
i recently bought a few black fin sharks and 2 of them have died just having them a day , i still had one after work , looking in the tank , it appears to be crystal clear , i have it treated to make tap water a livable environment for all fish, while i was finishing up some studying i happen to glance over and i notice he is having trouble keeping himself up right about an hour later he died also , what am i doing wrong , is there a certain temperature the water needs to be at certain food certain lighting , please help me all my other fish seem to be fine but all my black fin sharks are dying , please help i have one left and hes all i got, i need help bad please help, and please include some info on how to help guppies mate and additional info on them thank you very much  

Answer
Hi Vincent;

I need a bit more info to be able to help you;

What size tank do you have?
What is the water temperature?
How long has the tank been set up?
How often do you usually make water changes?
How much water is changed at one time?
When you added the new fish to the tank, how were they acclimated? (how long were the transport bags floated, how long were the fish in the transport bag before you got them in the tank, etc.)
What kind of filter does your tank have?
What other kinds of fish are in the tank?

Here is a web page about breeding guppies to help until I get your next email;

http://guppyplace.tripod.com/Breeding.html

At Your Service;
Chris Robbins