I tried a few different methods of removing surface scum in some nanos I had. I ultimately found that running O2 at night on a timer was the easiest and best method of eliminating surface scum. There was also an unanticipated side effect...my water is clearer.

These nanos are pressurized Co2 with glass diffusers and powerheads with sponge blocks for circulation/filtration/Co2 blasting.

Changes in PH are not as important as changes in TDS (total dissolved solids) because of fish osmotic pressure. When fish start dying people pull out their test kits. The most common test kit is the PH test kit. People use it and notice a marked change in PH, so they blame the losses on a ph shift. Since most people can't test for changes is TDS levels, they don't realize that the TDS changes affected the PH. PH is all they can see so they don't understand the underlying cause.

I'm definitely not saying PH isn't important at all. I'm saying PH is often the red-headed step child and sometimes takes the blame for things that it wasn't responsible for.