About the heater and pump....
Most hottubs have pumps and heaters made with stainless steel components. Stainless steel will not hold up under continuous exposure to seawater, and it's almost certain that the pump's shaft seal is not designed for saltwater exposure. You'd probably have to replace both with units with titanium or polypropolyne components (in other words, designed for saltwater use). Otherwise, all that metal will end up in your water.
While you are at it, you are going to want to check thoroughly for stainless steel screws used below the water line, and either replace them with nylon or titanium, or paint them over with marine grade epoxy.
Eco Reef Aquatics stocks all kinds of stuff that can probably be used as direct replacements, such as the inline heaters, etc.
