How many gallons did you come up with when you did the math?I got 659 but i might be wrong. Your on the right track but your going to need something bigger than a sump,something to put alot of LR in it alot cant be in the pond. I dont think you will need the UV sterilizer considering sharks cant get ich, it would just hurt your biological bacteria. a skimmer is a definate for a shark. I would have a good wet/dry or fluidized bed filter on it also, feeding fresh seafood realeases alot of ammonia into the water.