Well once again I'm certainly no expert but it is possible that you have GSF larger than 5 - 6 inches (I don't know what the growth rate is of GSF and since your pond is 2 years old oops I just noticed that you drained and renovated it one year ago perhaps the 5 to 6 inch GSF are as large as they get in twoone years, experts?).

GSF have much larger mouths than most sunfish and GSF can get good sized (we have had 10" GSF weighing close to 1 pound). It is amazing to see what a 10" GSF will strike, they will hit a 4" Rapala X-rap without hesitation.

A pond can only hold so many fish. Although buying larger predator fish (as opposed to fingerlings) would be more expensive you would not have to buy many of them for a pond that size. Buying larger predators would help to ensure that the predator fish did not get eaten plus the larger predator fish would begin controlling the GSF numbers immediately. (I can't believe I'm giving advice on controlling GSF, I think I must have a fever or something).

JHAP
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"My mind is a raging torrent, flooded with rivulets of thought cascading into a waterfall of creative alternatives."
...Hedley Lamarr (that's Hedley not Hedy)