Here is the reponse from Klaus from a question about the mini 180 and air intake. Looks like the higher the water level the more air.
This has been translated.
@Mirko.... the mini UC bring in principle more air, as if gelabelt is, a 180er can not at all only 800 litres air introduction have, but possibly also 1000 litres or even somewhat more. Always arrives on the water level, as deeply the mini UC is located dived in in the filter. The more highly the water level, the seriously more highly also the air introduction. These air introduction noises are extremely difficult to away-get. The resonator is there a very good possibility of decreasing the sound. In principle it is possible to clean-put in the muffler still cotton wool then the noise is again reduced clearly. In principle we are however opponents of cotton wool-plugged mufflers, because from own experience white I, adds myself the cotton wool very fast and should every 4 weeks be renewed. Therefore we leave the cotton wool outside. The resonator to mini UC is to be opened however. You can fill the resonator by way of trial with something cotton wool and schaun whether the noise is decreased. Otherwise reliably the double muffler solution helps. Luftansauggerue is actually audible with all Schaeumern, times more or less, present on the market. These noises are mostly over-sounded however by extremely strongly humming pumps. If one acquired then MINI UC, where the pumps are nearly noiseless, every other background noise, stop is noticeable extremely.
