You could try with the brush, but I bet it will eventually come off itself with shedding. I've never noticed any algae anywhere on mine but the shell. I wonder why yours has it. Is your filter moving the water at all? A little faster current may keep it down a little. Or maybe you have too much light over the enclosure. I only use a uva/uvb bulb on mine, no really hot basking light. He's near a fireplace which is on low all the time, so the water stays warm. Try raising the light a little, that might keep the algae growth down.