How to lower the pH in your freshwater Aquarium? There are many good products on the market for this… Check with your local tropical fish store and ask for there recommendations. It is quite often necessary to add quite a bit of these products to reach the desired pH level of say a 6.5 in your discus fish aquarium.
KEEP IN MIND*** DO NOT ADD THESE pH BUFFERS DIRECTLY TO AN AQUARIUM WITH DISCUS FISH OR OTHER TROPICAL FISH! pH SWINGS OF MORE THAN .3-.5 CAN BE FATAL TO SENSITIVE FISH SPECIES LIKE DISCUS FISH.
Add these products to your water change water before it goes into your aquarium, and slowly (over time) bring the pH down. Or preferably add them to an empty tank, to get your pH where you want it BEFORE you purchase your discus. One other note to mention, I have noticed that most of the pigeon blood Discus color morphs (Marlboros, rainbow dragons, tangerines, Apricots etc.) will exhibit much more peppering(black spotting) at higher pH’s. Another reason for the lower pH.