Research what a good Discus looks like before you buy them. Watch out for so called "good deals". There are more undesirable fish for sale than they are good ones. Things to watch out for are, large eyes on a small body, "football" shaped fish, peppering, misshapen fins, dark color, cloudy eyes, excessive rapid breathing, breathing from only one gill, stringy poo hanging from the anus, etc. Also, never get just 2 Discus, it is very stressful for them. They have a social, or pecking order, and need a group of fish to do this and feel secure. A good economical Discus tank would be a 55 gal. with a group of 6 fish, with a good HOB filter such as a AquaClear 110 using no carbon, and frequent vac and water changes.