Now think of the pH suddenly falling. It would feel sort of like being dropped into a vat of acid. When the pH suddenly falls to a 6.5 or below it is called a pH crash and is very deadly. Fish subjected to a mild pH crash suffer peeling of the skin, very similar to our sun-burned skin peeling off. We've seen cases of the jelly caps of fancy Orandas literally eaten away.
Sever crashes can end with complete fish loss.
In the case of an emergency a water change is in order or take the pH up quickly. A very clean system with little organics tends to be lower in pH. Bead filters, because of their efficiency, can actually contribute to low pH readings. Instead, it's best to use carefully prescribed products designed to raise the pH over a period of time and hold it at the desired level. We use pH stabilizers with great results. It's important to know that the stabilizers must be added back whenever water changes are made.