Live rock Help 20lb chunk

[donkey77]

ok so my LR had a **** load of po4 in it, its a big piece about 20lbs, i took it out of my tank, whats the best way to clean it, kill it, get the freaking po4 out of it, let it sit in the sun for a week, pressure wash it, its a boulder, i think iam going to smash it up to 2 or 3 pieces , i just don't know what to do with it, its a nice chunk but just to big, i battled algae for a year, and the algae won so i had to take it out. i did weekly water changes every week and never missed one, its a 34g tank with a 25g sump,
much help appreciated
thanks