With existing windmill and solar aeration in a 3 ac pond, evidently it’s is not enough when the pond has a duckweed problem that indicates a pretty high biochemical oxygen demand that consumes more DO than a “normal” pond thus fish kills occur. IMO windmill aeration is not much benefit of pond mixing beyond ½ ac and maybe 0.7 ac for a newish pond; and definitely not an old duckweed infested pond. Solar benefit will depend of volume of air produced and water turnover rate.
Duckweed is nature's signal that the pond is old and over enriched with too many nutrients mostly dissolved organic nutrients. (see later). I only see duckweed in old sludge filled hypereutrophic ponds. Continually chemically killing the duckweed IMO does nothing to stop the cause of the duckweed. Cause is way too many of the specific nutrient blends or chemical composition that stimulates the growth of just mainly duckweed. Your pond has duckweed and not plagued with bluegreen algae, nor plankton green algae, nor filamentous string algae nor even rooted submerged plants because the specific nutrient concentrations are very specific to growing duckweed and not the other types of plants at least not abundant growths. Basically in simple terms, every water plant species has a favorable chemical 'blend' to make it a predominant grower and other plants don’t really prefer that water chemistry. Change the amount and or balance of nutrients and duckweed goes away on its own, no chemicals needed.
I’ve seen bottom aeration operating strongly in duckweed and or water meal heavily infested ponds, thus aeration does not do a lot to reduce duckweed. Duckweed is driven by old over-enriched organic laden ponds often those that receive lots of leaf litter that is in various stages of decay producing those dissolved chemicals that favor duckweed. Another place that I most commonly see duckweed is in drainage ditches receiving septic drainage creating the over enriched water chemistry needed by duckweed.
More additional aeration may or may not stop duckweed growths,,,,,? however more complete pond mixing may help reduce the frequency of fish kills due to low dissolved oxygen (DO). Since you have existing aeration of solar and wind, if you add a shore based compressor,, I would put those diffusers in the main deepest part of the pond basin to get the best benefit from the new system. Move the other aerators to adjacent less deep water areas. Pond areas less than 5ft-6ft deep will usually naturally mix / circulate on their own and or get DO production if the water has 2.5+ft of clarity. Duckweed covering the entire pond severely limits sunlight penetration restricting oxygen production to ALL depths and areas. Thus DO sags are then common. .
IMO you will struggle with problematic plants of some sort in this pond continuing forward until you change the pond’s nutrient load basis or condition. Whenever I see duckweed in a pond, I strongly suggest a draining and bottom sludge cleanout. IMO Thick, deep high nutrient loaded, bottom sludge is the causative agent for duckweed. Draining and cleanout is not cheap but neither are the long term year's use of chemicals and contamination from repetitive herbicides to kill all the offending plants that are going to grow due to the high nutrient basis of the old pond. Nature is wanting to turn your pond into a swamp - wetland and a few hundred years later back to dry land again -
Aquatic Succession. Ponds are collection basins for anything that gets in the pond. Most all ponds have no flow-thru flusher which makes them age and fill in quicker.
I am not here "just blowing smoke" for you. Look where duckweed grows best and its uses. Growing abundant duckweed is a symptom of the conditions that favor its growth.
Use in high nutrient wastewater conditions
http://jeb.co.in/journal_issues/200704_apr07/paper_30.pdfhttps://academicjournals.org/journal/SRE/article-full-text-pdf/ADACD5329785Luxurious growth often occurs through active extraction of nutrients in sheltered small ponds, ditches or swamps where there are rich sources of nutrients, making the plant highly nutritious (Willett, 2005; Khellaf and Zerdaoui, 2010). Such characteristics have made the duckweed a useful plant in various ways.
USES OF DUCKWEED PLANTS - Duckweed plants are mainly used to reduce chemical load of facultative sewage ponds during waste water treatment (Vajpayee et al., 1995; Willett, 2005; El-Shafai et al., 2006; Shi et al., 2010; Bouali et al., 2012; Nayyef and Sabbar, 2012; Singh et al., 2012).
