I had my pond treated for the first time this year to control surface weeds and some bottom rooted weeds. I hired a well known local company who have been in business for a number of years. As I understand they treated the pond with copper sulphate and Sonar. This treatment was accomplished with a 6 wheel amphibious vehicle with a small outboard motor because there is no way to easily launch a boat in the pond. The point of entry into the pond at the shallow end is heavily silted. They fired up the outboard and stirred up a huge cloud of silt as they made their way to deeper water. Other than the muddied up pond there were no apparent problems with the treatment. The surface weeds died within 2 or 3 days. Hard to tell about the bottom weeds because the pond was muddied up. They returned 2 weeks later and retreated with the same chemicals. They also muddied up the pond again which had still not fully cleared up from the first time. I arrived the day after the 2nd treatment to find a muddy pond with 4 dead grass carp in the 17lb. range, 2 dead channel cats in the 4 lb. range, and a couple of dead bluegill, probably last years babies. I tried to call the company but they are closed on the weekends. I ended up losing all 6 grass carp and a couple more bluegill over the next 3 days.
When I finally talked to the company and explained what was going on they agreed to come out to test the water to find what caused the kill. The tests showed no overdose of chemicals but a very low oxygen level. I have never had an oxygen problem in the pond even during a serious drought, with very low water levels a couple years ago. They stated that the low oxygen would kill the larger fish first when I asked why no bass and very few bluegill had died. My question is whether the heavily muddied up pond could have caused the low oxygen level resulting in the fish kill? It has been about 3 weeks since the last treatment and the pond is just starting to clear back up. I think the first round of muddy water stressed the fish without killing them and the second dose of muddy water pushed them over the edge. Does this make sense?
