Instability on take off with hexacopter

My hexacopter is unstable on takeoff. When I apply throttle, at the point it is about to takeoff it looks like it is going to tip, I can just about control it with opposite elevator/aileron input, but its very sensitive and looks like it is going to tip in the other direction very easily if I am not careful. What could be causing this?

I have checked motor and prop direction direction and layout/wiring. It is all correct. I have calibrated the acceleromater and ESCs.

I am using APM 2.6.