leave all powerheads on 24/7?

[ScubaSteve]

As long as you don't have anything that has any major flow requirements it shouldn't be too bad. In fact I remember seeing several wavemakers and other control units having a quiet nighttime mode.

I personally have a similar set-up (aka the ghetto wavemaker) in my 20G using electronic programmable plugs from Wal-mart ($20! Have two plug sockets and they are more bomb-proof than anything else I have used) to control my two bigger K2's through out the day to mimic the directions of the tides (actually set to tide times... nerdy, I know...). So at my "simulated" ebb and slack tides, the only thing I have running for a short time is a koralia nano. Nothing seems overly unhappy with this, in fact some of my corals really started to flourish with this. If you have a lot of fish, I would be a little concerned with keeping the water turned over for good O2 concentrations though.

I'd suggest trying a night without the K3, see how things do. Then try a night without the K4 and see how it goes. Then finally give it a go with both of them off and pray. Oh, and don't forget to turn them back on again!