It is a combination of oils (from your hands/foods etc) and broken down protiens (waste, crickets etc). It's called a protien skim. add some massive circulation and it iswhat the white on the waves is. harmless- just ugly. It can be a sign that the water needs to be changed as there is more protien then there hsould be- also more circulation (with out creating waves *G*) can make it 'disapear' from site by recirculating it more through the water.