Look for a program relayrunner it free to download.
I use a printer port relay card on one system and a pci relay card on the outher. 0.000057 % failure or once a year replace the computer battery and have 0.0000000
the program is self restarting if power goes out. Also use a Dataq 16 channel data recorder. they have a usb 4 channel recorder for only 50 bucks if my memory is right.
PPm and Ph are dangerous to automate unless you realy spend the money on dosing equipment.
You can use a camera system to look at them over the internet.
I spend up to a month with out even looking at them. End of grow cycle 2 weeks and bloom up to 5 weeks. I have a 100 gallon system so they stay real stable.
I figure if industry uses it and its stable , go with what working for a few decades.