dya know you have the 3 trays where you have sponges + ceramic tubes,are they all lined up correctly? if so have you got the 2 bars the right way round[the bars that hold the 3 trays together]...make sure the 2 taps on the bottom are closed...you have 2 tubes in the fx5, ones long + goes to the bottom, that lines up with a hole in the top lid the 2nd is shorter, on that there should be a sort of rubber seal that clips into place sometimes that comes outta whack? if these are all correct i fill mine almost to the top...replace lid + tighten the hand nuts clockwise to almost as tight as you can get em, work ya way round then start again making sure they are as tight as you can get em using hand only otherwise youll damage the thread on the nuts...switch on filter and shake the whole thing for a few mins, this helps clear any trapped air...have you checked for blockages in the pipes?

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