As others before me have said, neither sharks or rainbows, nor CAE's, SAE's, and Otos, are good, compatible discus tank-mates.
Some grow too large, and harass and intimidate the discus, or are far too swift and active, having the same result of stressing discus, and others, like SAE's & Otos, may have a tendency to take a liking to discus' slime coats as part of their diet.
While others (like neons, for example) can't handle the higher discus temps, and soon perish.
One must be careful selecting tankmates for discus. Remember, discus are expensive fish, and their welfare & ongoing health maintenance must be the foremost concern for any discus-keeper. (Or you'll be tossing $$$ out the window.)
Some grow too large, and harass and intimidate the discus, or are far too swift and active, having the same result of stressing discus, and others, like SAE's & Otos, may have a tendency to take a liking to discus' slime coats as part of their diet.
While others (like neons, for example) can't handle the higher discus temps, and soon perish.
One must be careful selecting tankmates for discus. Remember, discus are expensive fish, and their welfare & ongoing health maintenance must be the foremost concern for any discus-keeper. (Or you'll be tossing $$$ out the window.)