The hat has everything you need, either as a connector or pin breakout. The ONLY weakness is if you need more than 9 pwm channels, because even though it has a built in pca9685, only 9 of the 16 are useable. That becomes a non issue when reef pi allows multiple pca9685 addresses.
I am not running co2, but im not low tech either. I run 2 beamswork lights and am putting 90 par to the substrate. Medium high light, overstocked fish. Lots of flow. The fish fertilize the plants! I have almost perfect water from my tap so I do a 15 to 20 percent water change every 1 to 2 weeks. Heck im trimming half a 5 gallon bucket of plants out every 2 weeks, I dont need more growth, lol.
I got my ph board from
@Jonathan Troutt and will only monitor PH. The ph driver for the board is not quite ready yet. But you can find details on the board in the links
@Ranjib just consolidated. JT bought a bunch of boards and the components and assembled them for a few of us, I think
@Diamond1 has one from him as well. Still up in the air on a ph probe, but the american marine pinpoint ph probe is the one that I have been researching. Good reviews at a decent price. You need to make sure its a double junction probe, and is rated for continuous use(in saltwater for reefers).
If i were to run co2, id love to just have reef pi be able to control a gpio output to a solenoid on the co2 system.