hey mate… congrats on your progress… im doing similar thing, but im going for multiple arduinos inside growbox (nodes), connected to one main esp32 (switch), and for multiple growboxes and room where they would be (more nodes) i would have one router - raspi - to have www control… im utilizing many open source projects, like PJON protocol for communication: https://www.youtube.com/watch?v=yPu45xoAHGg, DRO-Matic for nutes controll: https://www.youtube.com/watch?v=GlZHTMk3PBg, Mycodo for overall control: https://www.youtube.com/watch?v=nyqykZK2Ev4, and of course Adafruit libraries for sensors, Matlab channel for process control explanation: https://www.youtube.com/watch?v=ApMz1-MK9IQ, basically all i could get my hands on to make a solid product… i first made whole thing on Blynk platform: https://blynk.io/, which is very powerful platform to make IoT devices with nice mobile app, but since they pushed more of their business side, and less open source, and then released 2.0 version only for businesses, i went for different route, and to remake most of my things, and have offline interface via nextion screens and online via webpage, not an app… im nowhere near a programmer, im still on basic level of c++ and web languages, im electrician and am handy with tools, so i approached this with grow room design first, and then searched for solutions, and since there were many setbacks, and not enough knowledge (of control processes, desing of user friendly UI, grow room setup in general), i put my project on hold and decided to research the shit out of it until i go back to code… but i have a ton of info, some i already put here, other i can find for you, and share my experience working with arduino… ive mostly used arduino nano, cause its cheap, and there is ton of libraries for various sensors, but it has its limitations (8 bit controller with floating point simulator, so its very slow with lets say VPD calculation, which ive outsourced to my esp32), and arduino mega (handles 30 sensors without a sweat, but still 8 bit controller), so if you have a questions feel free to ask! also, about ph readings, youre right about probe being submerged, it has to be scientific grade to be allowed to be constantly submerged in a solution, and Atlas Scientific had one for 200$ (probe only, signal board is about 40$), but since many hydro users needed something less powerful but still resilient, they made cheaper probes with lesser resolution, consumer grade one has resolution and accuracy of +/- 0.1 and its 40$: https://www.atlas-scientific.com/probes/consumer-grade-ph-probe/ and their lab one has resolution and accuracy of +/- 0.002 and its 80$, both can be submerged in a solution indefinitely… hope this helps you and gets you some good reading material, have fun and happy growing! <3
Edit: example pic of Blynk