What is needed on a Digital Controller

[Psyire]

This is the kind of question that you probably want to ask yourself instead.

Some things to consider:

ORP monitoring (for use of ozone)
pH monitoring (for obvious reasons, multiple probes if your using a reactor or 2)
temp monitoring (sump, tank, ambient, etc)
salinity monitoring (obvious reasons, but I find it helpful to track how much salt my skimmer has pulled out in the skimmate)
timer programs (lights, kalk stirrers, solenoids)
water level switches (automatic evaporation topoff using pumps or solenoids)
Computer/LAN Interfaces (control and alarm alerting via. internet or stand alone computer)
SMS Interfaces (control and alarm alerting via Cell phone)
Dosing Pumps (control of and use of dosing pumps)
Redundancy (multiple floatswitchs, probes, programs, etc; Incase something fails)
Wavemaker (multiple powerhead control for wave/tide effects)
Sunrise/Sunset options (Dimming)
Seasonal temperature changes through manipulation of heater(s)
Water Parameter Logging (for each probe)

... I could go on but I think you get the idea