[Lampshade]

So looking around EBay the other day i managed to pick up a PLC cheaper than most light timers. So, i bought it, and started thinking of the endless possibilities of having a PLC for my tank. It's just a small PLC(8inputs, 2analog, and 4 outputs), its expandable to more, so i'll be keeping an eye on EBay for deals. While i wait for the PLC to ship i've started writing a program for it. I have a thermocouple/tranmitter, so i have temp readings, which i can put on the display. I've seen PH monitors, but i think i might be able to find something more usefull for that second analog, possibly Salinity, or something else. So far i Have:

-Light Timer - the reason i got it
-Over Temp. Shutoffs - Heaters off, fans on, still hot and the MH lights will turn off
-Feed Cycle - Main Pump off for 15 min, and future output for a auto pellet feeder
-AutoTopoff - figured i could make a cheap float sensor/solinoid setup
-Skimmer Full - Another cheap float sensor, that just pops up on the display when the skimmer's full


I've seen that other people have PLC's in their tanks, and my biggest question would be, what is worth automating? What is usefull? There's usually a way to automate something cheaper than a night out, so what would be a good idea for something to try?