Phase 1 was to add relays to the pump and heater so that they can be controlled by a microprocessor in the future. For the time being, just having the relay allowed me to use an AC->DC converter to trigger the relays with a 120V timer so I could schedule when it ran (and override that manually when we wanted to use it!).

Since I didn't want the heater to ever run though without the pump being on, I setup the heater's relay so it could only operate when the pump's relay was on. This was done by using a smaller 2-ch relay shield to power the 5v lines that went to the pump and heater's large relays. The 1st channel provided the power to the pump's relay as well as the power to the 2nd channel. The 2nd channel then was used to power the heater's relay. This way, both channel 1 (the pump) and channel 2 (the heater) have to be on for the heater's relay to switch on.