Actually you are talking about three different methods with three different purposes. Pump-airline to diffuser is for mixing deeper, larger volumes of water such as an entire pond 0.2-1acre. Venturi creates strong directional flow that is infused with bubbles for a relatively small distribution area. Air lift is a form of pump-airline- diffuser that creates directional flow as opposed to 360 degree distribution or spread of the airlift bottom diffuser. One has to match the method to the goal of what is needed.
BillD has the problem pretty well analyzed. Pumps and aeration will not solve the "weed" problem which is nutrient based. IMO the most efficient use of money and long term effort is to drain, deepen, and rebuild the nutrient enriched small pond. A pond of 4'-6' maximum depth with clear water is not much more, and can't be expected to be much more than a glorified weedy swamp-wetland unless one creates turbid water or applies a heavy use of algaecides or herbicides.
As mentioned don't expect aeration to control nutrient based plant growth. However the proper weed-algae eating fish could significantly reduce the plant growth and create adequate turbidity that would then reduce future plant growth while continuing to consume most of the recurring plant growth.
PS - Both of your surface aerators are in the shop because it is very hard mechanical work for a motor to constantly lift and throw high into the air water that weighs 40 lbs per 5 gallons. Motor burn out is common and should be expected.
PSS - ""Yes I was under the impression if it was duckweed it's a lack of aeration issue."" This is a wrong philosophy and contrary to the facts that govern natural growth and feature of duckweed. You may not even have duckweed which is another wrong fact.
Last edited by Bill Cody; 02/15/17 11:14 AM.
