I think I'll try out the ring ... I have tried turning off the filter during
feeding, but observed a strange thing. The fish don't seem to want to eat
the flakes while the filter is off, but the minute I turn it on they start
eating again. The filter does move the flakes around, so not sure if that's
any reason ...

Pavlovian response..

You can untrain them by ignoring their actions.
They'll understand when they get hungry enough
Bob