Yeah, adding in a chiller makes things way more complicated than just adding a resistive heater. A decent looking chiller for an aquarium is ~$1,000, plus you need temp sensors and control wiring to maintain the setpoint properly, and then you need to pray the electricity doesn’t go out. A 1/3rd HP chiller draws around 1kW including the circ pump

An aquarium backup battery for a simple pump is like $50 for something that'll last a few hours of outage, but for a chiller with that kind of draw, it's a bit more expensive.