Wha is wrong with the pump in my godfishes tank?

It's only cheapish pump....it sticks onto the side of the tank and there is a part hich is meat to be submerged...just a little hole....then there isthis pipe thin which sticks up to suk air in....it seems to be working less powerfully and knd of fades in and out....I took it out and checked it was not blocked..what else can I do? The power of the ai is too small to kep the fish happy. I dont wat him to die bt cannot get to pet shop for another 48 hours!