Here's my theory, maybe a little clearer. The rotting food is breaking down. It is made up of proteins. These are being eaten by micro-organisms that are making your water cloudy. The pH is probably dropping because the bacteria are breathing and releasing CO2. This would not cause an ammonia spike if you already have a srong bioload of nitrifying bacteria. What you are witnessing is a bloom of an entirely different suite of bacteria. Do water changes and make sure there is nothing left rotting in the tank. Throw some air stones on there for good measure. Are your fish gasping or breathing heavily?