I'm surprised no one has asked this yet, but how big is the pond you're fishing? How deep does it get? Is there structure around the shoreline? Etc.
As the days get hotter and the water temp gets high, it's likely these fish are holding tight to deep cover as Sam mentioned. Instead of looking for fish hitting the surface explore the bottom with jigs, carolina rigs, crankbaits, etc. to get an idea of where they might be laying low.
If the pond is only a few acres, I would guess they could learn your schedule if you're literally fishing everyday around the same time, especially if you're using the same presentations every time. Change up your speeds, lures, retrieve style, etc. Also, try waking up at first light and see if they're hitting then.
Tight lines.