Describe the algae in question, is it slimy or is it more like a bristly hair. Some algae like bryopsis(sp) can be difficult to completely remove. From a look at your full tank shot you also have cyno bacteria growing on your sand bed. The hard part of algae infestation is not the getting rid of it part, it is keeping it out after it is removed. I would suggest you figure out how you are getting so many nutrients into the tank in the first place. Is your water supply clean, are you overfeeding, or is your filtration just not able to keep up?