If you think that is a bad outbreak of valonia I'm glad I have no pics of my old tank
Hopefully something you've thought of... if you bleach the rocks your could have a massive die off of critters inside the rock which will release nutrients into the tank and make a whole bunch more valonia grow.
Wouldn't it be easier (seeing as how your taking the rock out of the tank anyway) to just manually remove it all? You might have to do that every couple of months for a while but eventually it would be all gone