How many discus in a 40 gallon?

Question
Hi,
i have 2 small discus and 1 rainbow shark in a 40 gallon.
(please don't tell me i can't keep a shark with discus. the shark is happy
sharing the tank with discus and is also happy with discus conditions.)

I am going to buy some fish from www.macsdiscus.com and i want to know
how many i can get.
the shark and discus are the only fish in the tank.
i most likely will be able to get a larger tank for them as they grow.

Thanks!!!!!

Answer
Hello Will,
Discus fish need 10 gallons of water each, so you could put 4 in your tank.  Discus fish are beautiful, but have special needs.  They live in acidic waters 5.8 to 6.8PH, and their water should be soft.  Make sure you have no ammonia, or nitrates in your water at all times.  Water changes are important.  Water temperature should be 82 degrees.
Rainbow Sharks are aggressive, and territorial.  The Discus is a cichlid, and therefore territorial too.  However, the Rainbow Shark as he grows older, could. and will stress the Discus Fish.  I would never keep a rainbow shark with discus fish.  A stressed Discus will stop eating, and once he does, it is almost impossible to get him to eat again.  The Rainbow Shark needs a 60 gallon tank as he gets quite big, with lots of hiding places.  He is taking up room in your 40 gallon, so if you decide to keep him, only one more discus is allowed.  Discus fish go well with schools of tetras, cory catfish...The Emperor Tetra is a beautiful fish that lives in schools and can be put in a tank with Discus fish.  I'm sorry, but you are taking a chance in keeping the Rainbow Shark with Discus fish.  It is always best to read up on fish before buying them, and trying to make get along.  They may get along in the beginning, but as they start to grow, things change, and troubles begin.  
Hope this will help
Lynda