YES flourish excel will kill fish when over dosed to much. I have done it.
I would strongly recommend doing a water change now if it is not to late for your fish already. The best way of using the over dose method that I have heard of on here was to:
1) turn off you filtration and use a small squirting tool like a syringe or small baster to just target the worst areas.
2) Take all the fish out and cut the light time down to around 4 hours then treat with excel and after 12 to 24 hours do a large water change 50% to 80%.
I hope this was helpful maybe someone with more knowledge on this can give you more ways to deal with the algae and not endanger the fish in the process.
I would strongly recommend doing a water change now if it is not to late for your fish already. The best way of using the over dose method that I have heard of on here was to:1) turn off you filtration and use a small squirting tool like a syringe or small baster to just target the worst areas.
2) Take all the fish out and cut the light time down to around 4 hours then treat with excel and after 12 to 24 hours do a large water change 50% to 80%.
I hope this was helpful maybe someone with more knowledge on this can give you more ways to deal with the algae and not endanger the fish in the process.
