My Discus fish are eating algae off of the driftwood in the aquarium.  Is this normal? Yes, this is normal and should be of no concern.  Discus Fish need some green material in their diet.  We offer our discus fish a varied diet of various pellet foods, which contain some vegtable matter along with the higher protein animal matter (shrimp etc.)  Try to give your discus fish a varied diet of frozen bloodworms, pellet foods that are designed for discus fish(try and get ones that are at least 40%+ protein content)... We offer HBH discus pellet along with severa made by Hikari...  Also turkey or beefheart based foods are great for getting good growth rates in your discus fish.  Saltwater fish foods can also be accepted by your discus with great enthusiasm and health benifits.  Emerald entree, and quite a few of the other foods are great.  Feed you Discus fish up to five times a day, with a minimum of 2 times.  Keep in mind... the more you feed the discus fish the more waste is produced.  This need to be cleaned up accordingly... water changes and regular filter cleanings.