Not ALL tangs eat algae! Hippo and Blue Naso's do not eat algae as a few other species wont.
Also scooter blennys do NOT eat algae. They need small critters live in the water to survive, copepods amphipods, baby brine etc.
I have a mustard tang that does a great job. If you truly have big tufts of algae, no one beats the lawnmower blenny. He literally will mow it down.
But be aware! LM Blennys have a voracious appetite and if they eat all of the algae, you will need to feed him spirulina based food or lettuce/spinach.