[unclejed]

To answer your question as to the merits of the overflow, the tank water level remains constant with no lowering of the water level. Another real beneficial aspect of the overflow is that the top 2" or so of the tank water are continually moving and with the help of power heads (I like koralia) there are no dead spots and no scum (proteins) that collect at the top hindering good water quallity. The constant "draining" of the tank to the sump (with a protein skimmer hopefully) assures an adequate turn over of the water as it is filtered, both from the live rock in the tank and in the sump (if you chose) or from bio balls. Contrary to belief of some, bio balls can not produce nitrates. If detrius is allowed to hang or amass on/in the bio balls, that creates nitrates. The same can happen with live rock so using fiter media (fiber) in the drip tray eliminates most detrius from reaching the bio balls or live rock. So, the overflow is the way to go as far as assuring one of the best ways to purify your tank water.