heres the thing I notice (now I would almost need to see it in person to actually see how its wired) but if you have for example the sump setup.
non-gfi breaker-----GFI outlet heaters------GFI outlet return pump------GFI outlet skimmer-------GFI outlet doser----GFI outlet light-----GFI outlet open-----GFI outlet open.
Say your away for the day and all the GFI plugs are wired on the Load side starting from the heaters. If the light tripped the GFI and it actually went back and tripped the Heaters everything down the line would be off not saying it would happen but hey I have seen some weird things happen before (I tripped a dedicated lighting circuit in a panel downtown and took out the MAIN breaker for the building).
So if that whole circuit is off for a day you have just lost, heat, skimmer, return, doser plus whatever else you want.
But then again if the guy wired them correctly so they are all separate then if you trip the light plug the rest still keeps going. It all depends on how they are wired and its easy to screw up if your not paying attention.
My suggestion would be anywhere you have a "GFI Outlet lights" change it to a standard plug no GFI. Ballasts trip GFI's randomly and if your lights are on a timer and your not home its asking for trouble.
My whole tank is on 2 circuits in my house and I dont use one GFI plug or breaker. I have standard plugs with drip loops on all my cords. Thats just how I do it, everyone has there own ways.
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