Nothing, just install reef-pi and play with the user interface if you want to get a feel for it. Then from there on decide what you want and start working for each of those things. Here is my list of recommendation on getting things, sorted by complexity (easy to hard)
- get a Kasa hs300 and automate power control , not that you need it, since it has app already, but this will be the foundation for everything afterwards
- get a float switch, a 10k resistor and a small pump, and automate ato. Monitor your daily ato usage, setup alerts etc. bring all your tank equipment ( return , heater etc) under reef-pi control, setup some macros to ease tank chores like water changes that requires shutting off things in particular order.
- get a ds18b20 sensor , a 4.7 k resistor and automate your temperature control
- light automation..
- ph monitoring…
