This is an additon to Bob's post of Nov 22. He mentions that "aeration, from the bottom up, creates vertical currents, effectively mixing your water column". This is true but for novices it is a little misleading if you take it as complete fact or truth. The bottom diffused aeration and the resulting upwelling boil has only just so much "reach". The amount of reach or the resultant effective mixing area has LIMITS. The mixing boil cannot spread water out from the boil indefinately. The amount of reach or spread is dependent on the strength or size of the boil or rising column of water. Obviously the bigger & stronger it is the larger and more effective the spread will be. One small, continuously mixing column of water can not effectively circulate a, lets say a 10 acre lake. Plus a simple bowl shaped pond is also easier to effectively circulate than say a pond with an island, embayments and or heavy weed cover. All act as baffles to block, deflect, and hinder water flow and movemnet.
