I agree with Bob's assessment and Cecil could also be right that the cold rain added to the DO reduction.

However let me add one more to the mix. CuSO4 in low alkalinity water can and does kill fish even in low amounts. The combo acts to inhibit gill function and the fish can't breath. The fish gills work but they can't uptake O2.

http://www.pondboss.com/forums/ubbthread...=true#Post35566

Last edited by ewest; 08/23/09 06:22 PM.