Yes, I have killed fish in the past with the algaecide, but the problem was I extremely overestimated the volume of my pond and horribly overdosed it. But I really don't like to use it. The fish are sluggish for 24 hours, and I can tell they really don't like it. Unfortunately plant selection in my local places is mediocre. I ordered a lot of underwater plants online yesterday, and some weights to sink them to the bottom. And the fish will like them also. The algaecide actually worked really well, I can see the bottom clearly this morning and the fish are back to being happy and active. My hope is that the plants, once the growing season gets fully underway, will keep it that way. I will not use the stuff again, I really do fear it.
By next year, i will have to find a way to relocate some fish. I may not be overstocked now as the little fish are still quite little, but they are growing quickly and I can already tell there will be more on the way. I may need to add additional filters, my pump can certainly handle the extra load. It's overbuilt for the pond size.