New user, so bear with me.
I know of a system used to keep seawater cool in a tank containing crayfish.Above a certain temp the crayfish get too aggressive and fight.
Condensing unit is a hermitique from memory,running on 409a,has TX valve.
Evaporator is a long length of copper tube inserted into a larger diameter plastic tube and the plastic tube is filled with vegatable oil.(A bit like a tube in tube condenser).When the evap comes out of the tank the plastic tubes are sealed.The length of this evap is quite long but you dont see it because it is hidden under the rocks and sand under the bottom of the tank.System works fine and does the required task quite well.There is another tank which has a titanium tube for an evaporator placed directly in the water.

Regards