best way to get old dead rock white again???

[clipperfish]

Hello . I bought some live rock from someone .awhile ago and it was covered in green alge and hair alge . what i did was cook it for three months in a tub of saltwater with no light at all .the alge disappeared altogether .And I change 50% of the water weekly .it might not take that long but i was moveing so i left it for three months .hope this helps .