I have a few questions. I bought a second-hand Tunze 9410 AC and it doesn't come with a filter sock. Do I really have to have Tunze's or are there other brands / types that fit? I see that the silencer is under water on all the videos on YouTube and here I read that it must be above water. How about that now? Can you also control the height of the water in the skimmer without using the adapter with filter sock?