Pea gravel will work but 3/4 rock would be better. You might want to wash it again when you get home with it. One way to do that is to just put the hose on the pile and take the cleanest stuff off the top and work your way down.
Also that pond is huge in terms of aquaponics so not sure if there will be enough fish waste to feed the plants as it will get dispersed unless you have a lot of fish. The Ducks might help but hard to tell.
Fishy may know something I don't.
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