What are these? I'm trying to get my head around the first 2 systems and how it would work with a wet dry filter... now with the filter if i were to home make one, does it mean that the filter media shouldn't have water present around it?
i'm abit confused about how the whole wet dry works.. i know that water is meant to drip down onto the media so that it gets oxygenised and then the water gets returned to the tank via a pump, but not really sure if the media is meant to be constantly dry.