This is to demonstrate how much water flow I have down the length of the tank, it's a 5ft tank. Circulation is via the long spraybar at the back of the tank coming from 2x 1400lph external filters, a 600lph internal filter at the left hand side of the tank and also a 1600lph power head, (wave maker) also on the left and just in front of the internal. Good circulation is essential not only for the general health of the tank in avoiding any 'dead spots' but it's also essential for the plants and for the circulation of the pressurised Co2 being injected into the tank. As a side note, most of the Discus are gathered at one end of the tank because they are looking out of the room window, seems to be a favourite pastime during daylight hours!