I used Excel for the first time last week. Followed the initial dosing instructions on the bottle and I think it's too much. The little algae I had growing on the top of a piece of driftwood died off quickly. It also made the water cloudy.
I also heard that the cap is actually more than 5m. I didn't test it, but it might make sense since overdosing the stuff is known to kill algae. I dose less than what the bottle says, every two days now.