Bought a adjoining property with a 2ac pond. In spring we found out that we had a really bad pondweed problem covering about 20% of the surface and making it largely unfishable. I tried Diquat per the 2 week waiting period but found that I couldn't keep ahead of it, they were blooming again before the time for the next application. I went 'nuclear' applying every week a pretty heavy spray and finally started seeing results. Before I ever started I installed a 1hp aerator and I was running about 6hrs a day. towards the end of the summer fishing went from mediocre to bad. We haven't seen any dead fish but we didn't catch many. the last couple months we have caught no bluegills at all. I caught a few bass with a plastic frog pulled through the remaining weeds. The water is dirty, it will dye your skin if you stick your hand in the water. I stopped spraying about 6 weeks ago and though I was concerned about the water I assumed the aerator was taking care of the oxygen depletion. I think I overestimated the capability. I finally got a meter and tested the water at about 45%. I increased the aeration run to 24hours a day for the last several days but its even lower now - around 25%.
Because of lack of rain we have had almost no turnover of the water in the pond. I am guessing at this point the only thing that's going to fix it is enough rain that a significant portion of the rotting weeds gets flushed. I'm not sure if the aerator is actually making things worse but it seems like it.

Mike:

What are your O2 readings in ppm or mg/l?

Aeration is a funny thing. It needs to be sized to the pond and to the amount of water that is in the pond. Do you know how many times the aeration system brings the total pond volume of water to the surface?

the mg/l is in the high 3's to low 4's. The aerator is 6.7 CFM. I haven't calculated the total water volume its right around 2ac with avg depth of around 6'

Unless you know the lifting GPM or GPH of the diffuser (s) it's all a guessing game.(Meaning knowing how many GPM/GPH the diffusers bring to the surface for every minute/hour of run time) You can go out and measure water temp to see if the pond is homogenized temp wise, but we are getting close to turnover temps so that may not do you any good.

If you can measure O2 levels, go out to the deepest part and measure the O2 in 2 foot increments depth wise and let us know what it is.