The concept of aeration isn't about aerating, strange as that sounds. Aeration, in our pond management scheme of things, is about moving water vertically, where it can contact the atmosphere to release its gasses and absorb oxygen from the air.
To that end, as long as ALL your water (or at least most of it), contacts the atmosphere often enough to make that healthy exchange, aeration can be part time.
To that end, it isn't an "all or nothing" thing. It just needs to be "enough".
An older lake with lots of nutrient load needs more aeration than a young lake with more sterile water.
