Cool that you are thinking ahead on the components needed to build your system.
A couple of notes: This appears to be a thermoelectric chiller which are somewhat inefficient. What they are giving you for power also appears to be the power at the wall plug.
In refrigeration applications, thermoelectric junctions have about 1/4th the efficiency compared to conventional means (they offer around 10–15% efficiency of the ideal Carnot cycle refrigerator, compared with 40–60% achieved by conventional compression-cycle systems
This would equate to less the a quarter of the 180W as cooling. Or, <45W/hr of actual cooling capacity.
Which make this particular chiller appear a bit underpowered for ~40 gallon system. Of course, it really depends on a variety of factors including the temperature of the environment (with lights on), the desired temperature of the solution, and the time required to pull down the temperature.