Jesus--yeah that is the objective to "cooking" the rocks. Since you noice that the algae is receding a bit and the sugar dosing and bacteria doing it's job, I wouldn't take out the rock just yet.
Cooking rock is only a last ditch effort when nothing is working and all measures were taken to fight the algae. In your case, it sounds like you did get some "dirty rock". However, from the sounds of it, the sugar dosing is helping. I would keep up with the sugar dosing, eventually, all the PO4 in the rock will have released because of the bacterial colonies combating it.