For some reason the thumbnails wont open....probably my computer.
But from the info above, it sounds more like bacteria or cyano though cyano tends to represent more of a mat than a clump. Is this how it grows---it looks white, which if this is the end product, may be the dying stage of hair algae which can be removed easily. But if it grows white, slimy, and easily removed it is not HA.
How old is the tank, water parameters, lighting schedule (if mh or t5, how old are the bulbs), feeding schedule