What Maintenance do you need to do to keep Discus Fish - Reverse Osmosis or not! 

Its an @ProfiLuxGHL Profilux 4, highly recommend

I don't believe you need to panic about pH. Mine has been down to 4.5 and back to 7 in minutes if you add some kh. Fish were fine. If your really worried add some coral sand to your tank and you pH won't move.

@@discus.switch Aragonite or crushed coral is sometimes employed for KH and GH stabilization, however aragonite and crushed coral (as with Wonder Shells) only stabilize KH (they are poor buffers, especially crushed coral) and should not be used in place of a true KH buffer such as Sea Chem Alkaline Buffer when true buffering is necessary due to fluctuating KH or pH whatever the cause may be.

@@discus.switch The bottom line is that Crushed Coral or Wonder Shells MAY help maintain KH/pH in a low bio load aquarium, they are best used for minerals (GH) and even here the Wonder Shell is far superior do to the fact it dissolves at a much faster rate and reacts much quicker to chemistry changes in the water than does crushed coral. Besides the simple mineral makeup of crushed coral, tests (especially in marine aquaria) show that its use to increase KH simply is poor!