i'm starting a new tank, and i want some info on how to get the most out of natural filters. the tank is a 3 foot by 18 by 18. I also have ten kilos of marble chips, a penguin 175 bio wheel filter, an ip 3 pond pump for circulation, an airstone with pump, a hundred watt heater and a two foot ballast with single tube. the tank is only half full coz i didn't have enough salt to top it up, and the heater isnt powerful enough. i am saving for a two hundred watt and a bag of salt. i recently got a peice of live rock, and it is really cool Any ideas on what to get next would be a great help. i also want to have most of the water filtered naturally.