Hi My Biomaster 600 Thermo filter has a habit of sucking air through the seals, when the pre-filter becomes slightly dirty. The air comes out through the hose-outlet at regular intervals. The frequency of air coming out, increases with how dirty the prefilter is. If it only did so, when the prefilter is significantly dirty, it could be regarded as practical, as it is an indirect information on that the filter needs to be cleaned. However it is quite anoying that it also does it, even though the …