IMO not a sound decision. The pump is not designed to contact corrosive chemicals, does not use household AC, may contain copper, unnecessarily complicated, and is low flow to boot. It might be built better than the average aquarium pump but you have no idea how reliable it will be in SW. Small amount of corrosion could bind pump, or the seal could fail.
I think the biggest mechanical problem you would encounter is rapid damage to the rotor thrust bearing. The material is unsuitable for contact with SW and you would likely see runaway erosion-corrosion on the face.