Why don't you clean the algae yourself?
I'd never keep an algae eater in a discus tank, discus are fragile and very sensitive to poor water conditions. Plecos (whch would probably be your best bet) tend to be a bit boisterous when they're not hiding, they'll dig up live plants, not to mention how much waist they produce, which, IMO, is a lot more harmful and pesky than algae.
If you're too lazy to give your tank a good scrub down of algae every now and then, then you're too lazy to keep discus, if you ask me. Even with algae eaters, it's recommended that you give your tank a good cleaning of algae now and then (which is why I personally don't keep algae eaters. I find them to be more of a nuisance than a beneficial cleaning pet, so I don't bother.) that's your job as a fish owner, to keep the tank clean, not the fishes.