shark pond probably means saltwater
i would think for something that big a series of simmers would be your best bet, but not in circuit, parrallel.
put an airstone at the bottom of a two litre with a siphon from the tank into it with a pin valve and then an overflow with a valve going to your sump
Why don't you just replicate the skimmer you made for your 55 gallon, but just scale it to size for your pond? It shouldn't be that hard, right? Or am I missing something...?