I use a PLC to run my reef tank and it is excellent.
I have the following setup.
Inputs
1) Skimmer on and off - switch
2) Skimmer off - 60min - push button
3) Main pump on and off - switch
4) Main pump off 20min for feeding - push botton
5) Sump level switch - turns on the small pump in top up tank
6) Low level sump level switch - if the sump runs dry it turns off all pumps, reators and skimmer.
7) Top off water container level swith which turns off the soliniod connected to the main water tap.
Outputs
1) Main pump
2) Skimmer
3) Ca reactor
4) Zeovit reator
5) Top off tap soliniod
6) Top off pump
I am is South Auckland if you want to have a look.