As 'jeffhasapond' said, I too usually do about 20-25% at a time. I did mine last week with some cutrine and had excellent results...just have to be careful. I've done it myself for 3 years now with great results. Sounds like the hired guy overdid it, I don't know how big your pond is, but I would do it myself next time. I stray away from the copper sulfate at this time.
