ATS are great. There are several ways of doing them, from the old 'dump bucket' to the new vertical flow versions. They are a very simple method of filtration that I personally have not seen any downfalls towards as they will filter the water.
They are simple to build, I made the one on my 55 reef out of an outdoor pamphlet holder and PVC
. For one that would be filtering at minimum 180 gallons of water, it would need to be much larger than that, obviously.