I don't use Aquaclears anymore, I prefer the canister filters now, but when I did I too encountered the issue of the AC's not starting consistently after a drop in power. What I found helped the situation was to ensure that the tank level was above the bottom of the siphon pipe, the one that leads to the impeller. This keeps water in the inlet pipe when the power cuts out, and the siphon does not have to be restarted, i.e. when the power is off the flow does not siphon much water out of the filter and the intake does not suck in air.
I will say it is only a partial help because once the filters aged a bit the impeller could jam against the housing, the only way I found to deal with this was to poke the impeller with my finger.