AC filters will tend to overflow on the intake side a bit if you have it on full flow. This is nothing to be concerned about, everything from the mini's to the pair of 300's on my oscar tank do it. They will do it more if you double up on sponges, a common trick.
Sometimes to get them started you have to give the impeller a little spin, especially if it is a little dirty. If you have skinny fingers you can reach it, I have fat fingers, a Bic pen works well for giving it a little poke.
The AC filters are tough little buggers, my oscar ripped off an intake sometime yesterday. Filter drained back into the tank, as the intake was pushed up from the impeller. Filter ran dry for who knows how many hours, motor overheats, thermal protect kicks in.
Unplug it, fill it with water, replace the floating intake. Plug it in, poke the impeller with a pen, starts right up.
I think my oscar has anger management issues.