I want to set up a 240 gallon discus aquarium?

you could have a bare tank, but you wont keep plants unless you put them in pots which would look stupid, also i try to replicate the environments as closely as possible, so for me its not an option, but if you were to you would have to bee pretty bone idle. get gravel, then you can use a gravel vac to glean it, its a doddle and easier than sand. to hide the intakes, id use rocks, or bogwood, i usually have well planted tanks, and the plants grow up to cover the inlets, not block them, but keep them out of view. the trouble with a foam rock scape is that although its easy enough, if you mess it up, then it can knock the ph up to about 10, no more discus, you have to either cure it, which can take months, or seal it (look up g4 pond sealant) but this can wear off after about 4 years at which point the cement will leech chemicals if not cured and kill the fish.