When keep caridinas like CRS for example, you need constant temperature. when you off your aircon, temperature can go up too high, and morning you turn back on your aircon, temperature fluctuates too much.
fluctuations of temperature, or water perimeters will cause shrimps to die because they are quite sensitive to changes.
Getting a chiller makes temperature constant. which is why shrimps will thrive. temperature also cannot be too low because it will decrease metabolism for the shrimp, your shrimps will grow slower, but at a lower temperature the colours will be very nice.
if your temperature is too high, they shrimps will look like they will have colour loss, and too hot they cannot take it. especially caridinas. thats why 25-26 is the optimum temperature, in my opinion.
Working at Aquarist Chamber has taught me all these, although i do not keep shrimps personally at home anymore