Any suggestions on a starting overdose amount? 5X the recommended amout to start?
I would Not recommend it at all, you will kill many things, it is a herbicide actually, but is selective at lower dosages to algae.
So you will kill all the inverts and the fish, then the plants.
Wiser to give it more time, wait a week etc and then see.
More is not usually wise with these types of herbicides.