PH: Discus must be kept at the lower end of the ph scale, we recommend a ph of 5.5 discus can be kept between a ph of 6 and 7, however many bacterial problems often occur at such a ph. At 5.5 bacterial skin infections don’t thrive and many skin problems are averted. I remember at one time we had two 8x2x2 and two 6x2x2 fish tanks on the same filter system, in each tank were 500, 3cm discus very overcrowded, yet everyone of the 2000 discus were very hungry and healthy. It was obvious the ph was right. When the ph was checked it was 3.75, since then we have favoured the lower end of the ph scale with very good results. We use hydrochloric acid to lower ph, this can be purchased from Bunnings or other hardware stores sold as concrete cleaner. When your water change is due treat the fresh tap water,.before placing it in the aquarium, we use plastic garbage bins for water treatment. Fill with tap water, add chloride neutraliser then hydrochloric acid; about 1ml at a time. Some water types keep buffing back up, but persistence will pay off. This acid burns the skin so be very careful, try to stabilise the ph at 5.5 Place an aquarium heater in the garbage bin and heat the water to 28 degrees Celsius with the aid of a power head and hose, pump the treated water into the discus tank, this way there is no ph or temperature shock. We place a small amount of coral rubble in the discus tank to prevent a ph crash.   Warning Hydroloric Acid shold be used carfully. first mix 100ml of hydrocloric acid with 900ml of water this makes a 10% solution it is still very strong . use only in small amouts like 10ml at a time for tanks under 3' use 1ml at a time and bring the Ph down slowly please be carefull