Rollo, the green algae is from your hose pipe, when water is left in the line and out in the sun this happens.

Regards the pump, turn a tap on in the house, plug it in and you should hear it start trying to pump, if no water, remove the white outer case and there should be some kind of bleed screw on the water line, usually at the highest point on the pump. Unscrew this slowly and air should come out if it is air-locked, hope this helps.