Spot treating with Excel will kill algae. Also, using dosages in excess of Seachem's recommended dose when using Excel as a carbon source, has been found to control algae.
In my tank, I used Seachem's recommended dose - and found that it exacerbated my algae situation. I have not tried overdosing Excel in this tank.
I didn't realize you had to overdose it though. So I'm probably making my algae worse then? Cause I just starting adding it per dose instructions on the bottle. I mean I know about overdosing it, but I didn't think you had to do that to kill algae. I though you could just start using excel and get your co2 stable and everything would balance out. So I guess I read something wrong then.