For both level and temp, a long delay between sensing is OK most of the time (twice a day, maybe 3 or 4 at most), when the value is not changing rapidly. But when filling or draining the pool, or when heating the pool, the value is going to change quickly. So - put the system into Deep Sleep, turning off all but the RTC Controller, and wake it up using an external signal. A float switch that will detect when the pool is too high, and another that will detect when it's too low, can send 3V to a GPIO to wake up from Deep Sleep. (https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/sleep_modes.html#external-wakeup-ext1)
When heating the pool, I want to know when it reaches a pre-set level ("the hot tub is ready!"). This is possibly a somewhat different project from the current Transmitter, or maybe a fork from it: use some buttons to move the set point up or down, and a button to turn off "active monitoring" (return to Deep Sleep); use a display to show the set point and the current temp; send the temp to the Base Station every X minutes during heating, and send an alarm when the setpoint is reached; after sending it a few times (to make sure it's received by the Base Station), then go back to Deep Sleep. As a failsafe, if it doesn't reach the setpoint after 2 hours, go back to Deep Sleep.
For both level and temp, a long delay between sensing is OK most of the time (twice a day, maybe 3 or 4 at most), when the value is not changing rapidly. But when filling or draining the pool, or when heating the pool, the value is going to change quickly. So - put the system into Deep Sleep, turning off all but the RTC Controller, and wake it up using an external signal. A float switch that will detect when the pool is too high, and another that will detect when it's too low, can send 3V to a GPIO to wake up from Deep Sleep. (https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/sleep_modes.html#external-wakeup-ext1)
When heating the pool, I want to know when it reaches a pre-set level ("the hot tub is ready!"). This is possibly a somewhat different project from the current Transmitter, or maybe a fork from it: use some buttons to move the set point up or down, and a button to turn off "active monitoring" (return to Deep Sleep); use a display to show the set point and the current temp; send the temp to the Base Station every X minutes during heating, and send an alarm when the setpoint is reached; after sending it a few times (to make sure it's received by the Base Station), then go back to Deep Sleep. As a failsafe, if it doesn't reach the setpoint after 2 hours, go back to Deep Sleep.