You are asking for problems if you put ottos with discus. I had them too in planted tanks. they will harass the discus then finally start attaching. They may not do it for quite awhile but they will eventually. and as Mat said they will stress them to a point of weakness. I have had bn plecos for many years in many different tanks and never have i seen one even harass the discus. plus the ottos do little to keep algae in check. find and lower the source of algae first then use bn.
Jim
1250 bb pot-planted: twelve discus (six my babies), cardinal tetras, sidthimunki loaches, angelfish. 35 gallon hex tank: hospital40gallon grow out tank: snakeskin juvies