Discus are specialty fish and need to be taken care of properly. Special needs, big tank, lots of room, everything set up especially for them, lots of little details, temp light foods, tankmates, etc. If you aren't doing 30-50% water changes daily because of frequent feedings, and their needs for pristine water, there is likely a problem with how they are being raised.
They are a majestic fish and are a HUGE amount of work to raise from small/young size/age. Brookster knows as he is raising numerous babies in lots of water and caring for them the way they should be raised.
As for algae, good light and not too much time on and clean fresh water will help.