I too have had to add an air pump to the air intake of my T100multi.
The pump was drawing air ok for the first year then decided not to anymore. I had to re-route the main plastic feed pipe to the skimmer to get it to fit the tank. Now if the pump is placed in the water at the normal place, no air is drawn in, if the union in the plastic pipe is uncoupled air is drawn in. One thing worth remembering is that all pumps loose a lot of efficiency after the first year of running.
The other porblem that you may have with the T100 is that if you switch the pump of to empty the collection cup, when you switch back on NO air will be drawn in. You then need to remove the pump and drain the water out of it and put it back. This will usually get the air intake working again.
I have to disagree with Gary about the bubble size issue. If you pump too much air through the intake you will notice that the flow rate of water through the skimmer will reduce. If you keep adding more air, the pump will stop pumping water and air will escape from the water inlet.
I would also recommend a word of caution with the UK Aqua-Medic importer. I have had many dealings with them and found them to be very arrogant and quite often wrong. I have had a very dissatisfying and very expensive experience with Aqua-Medic which resulted in me purchasing a piece of euipment that does not work as good as they said it will and they never offered me any refund/replacement. Also the LFS I brought it from said that because I brought it on the direct recommendation from Aqua-Medic, they would not refund me any money either. We are taking over £400 here!
If I was honest, I wouldn't touch them with a barge-pole. even some of their stockists don't speak too highly of them.
It's just an opinion though..........with the added experience