Peter
i dont think i made much sense in my post about 7000litre pumps i was talking about water pumps .
The air pump was a different issue . i used to provide the air to the air stones in my tanks by a koi air 65 ,they have 20 outlets mine never faultered for the two years i had it.

Also the huey hung sponge filter has a vacuum device inside it which sucks water in through the sponge trapping any debris left over food etc the air then expels through the tube on the top taking with it any harmfull gases and also providing surface movement on the top of the water . personally i think they are great for smallish tanks but wouldnt use them in big tanks unless i was running a sump also.