Protien skimmer help please

My proteine skimmer is not working properly.
I have cleaned it out but its not producing enough bubbles.
Its a pump fed skimmer with a venturi, located inside the tank, with the collection cup just outside of the water.
Its not getting the bubbles/dirt from the water as it used to be, i was emptying it every 3-4 days before but now its been about a week and its only got a dribble in the cup.
Its only a small unit for a 14gall tank, I was sold it with the tank.

My ideal solution would be to buy a proper external one for a bigger tank, should i wish to upgrade to a bigger tank later on.
Problem is, i cant afford it at the mo!
Would it be ok to use an air pump in the bottom of the skimmer to get the bubbles?

Thanks, thats put my mind at rest. I will still modify it though just while i can save up for a good one. It cant hurt but may help a little
I did panick though, i thought it was an essential bit of kit for a marine tank.

From what ive learnt so far, marine keeping is not as bad as what people tell you.
Yes, the initial startup cost can be off putting, but when youre there, provided you look after things as you should, its not very high maintenance.
Saying that, i only have a small tank so cant comment for a bigger setup although i was told to get the biggest setup i could afford to ease the maintenance.