Just don't put sockets and switches over the tank. I know that in fishkeeping it is sometimes complicated to follow all the electric safety standards, but try to do so as much as you can.
I'm using 2 amps circuit breakers for light and filters and 6 amps for heating (on 240V AC). I also use a residual-current device and three wire setup. One RCD can be enough if you don't run a fail-safe duplicated design. I have also connected all metal parts with a PE wire.
And no, I'm not using waterproof sockets because they tend to stop to be waterproof when you plug anything in.