I did not want to hijack mr Pope's thread so I am posting again after Bluboys questions.There are so many myths about these fish,things like 6 week matured water,soft water,PH and so on.
Discus are a Cichlid and like the rest of that tribe are pretty robust,what you need to do is keep it simple.
To rear and keep discus use HMA water,keep the temp around 30 degrees,feed them good quality food and buy a group of fish not two or three,but six or ten,or more.Sponge filters are fine but I use cannisters with a pre filter on the intake,then water change as often as you can,Hma the water aereate it, use it,simple.The little one I am bringing up get 70% change daily,and thats it really,I bet there are loads of people that wont agree but I would only worry about water parameters when trying to breed these fish.Regards Ray.