Discus requires a strictly adhered to water change regiment of at least 25% every week. Discus are very sensitive to water fluctuations so make sure to test any water going back into the tank. Make sure when doing water changes to carefully vacuum the substrate thoroughly. Before vacuuming use a sponge or algae magnet to clean viewing panes and once the removed algae has settled on the bottom start vacuuming. Take great care when cleaning the tank to not cause unwarranted or excess stress to your fish as they are very prone to stress related diseases.