The HAQOS EX1500 sucks water from the sectioned tube that is build into the filtration stages and goes all the way down.
This filter circulates water through the stages from top to bottom.
Once water reaches the bottom it's sucked up via the tube. THIS IS OPPOSITE TO SOME OTHER FILTERS IN THE MARKET.
Therefore you should put carbon at the bottom, Biological media in the middle sections, and the physical filters (coarse and fine foams, and sponges) at the top. Between the foams - the coarse foam (I think it's the supplied blue) should be on top of the fine foam (Black), and if you have finer filters they should go below that.