So you've got your lights, co2, and nutrients dialed in. CO2 is maxed out, you're dosing EI(or whatever), and you've gotten to the point that BBA and string algae aren't constantly covering your tank, but there's just that last bit of algae that you can't get rid of, but you consider it unsightly. Well, there are a few ways to deal with that. For starters, glutaraldehyde/Metracide/Excel (Glut from here on out) are excellent method of algae control.
Glut can be a great way to help speed up the destruction of algae AFTER you've slowed and/or halted it's growth by dialing in your lights/co2/ferts.
A planted tank blog has completed a case study using glutaraldehyde to eliminate BBA. You can read about it here:
Their method is fairly similar to mine.
When I'm spot treating BBA with glutaraldehyde, I make a 1:4 dilution (that is, 1 ounce of glut and 4 ounces of water) and put it in a spray bottle. Then, during a water change, after I have drained the water out, I spray that dilution directly on the BBA and let it sit for about 5 minutes, then fill the tank up. Within 30 minutes the BBA turns white, and flakes off and disappears within a few days.
This method also kills GDA and GSA on the glass, hardscape, and plants.
However, be careful because not all plants respond well to this strong of a glut solution. I'm sure this list is bigger, but in my personal experience, rotalas, mosses, and vals do not like to be hit with this solution. Again, in my experience, Crypts and Anubias(two that are prone to GSA) respond positively to this solution.
For more information, that is an extensive sticky about this subject: