I have been dosing my 30g FW one cap and 3g and 5g shrimp tanks a partial cap every other day. So far so good. I do want to get an eyedropper for better control.
I dose 4ml daily in my 29g with no negative effects on the malawa shrimp in there. I dose 2.5ml daily (previously 3ml) in my yellow shrimp tank with no negative effects there either.
That said, in my experience, thread / hair algae doesn't really care much about excel. The only thing that got rid of it for me was hand removal, reduced feedings, and more fast-growing stem plants to out-compete it.