How could I get rid of Grape Macro Algae!

[RESONANCE]

Yeah, grape caulerpa (what you have) really gives macro algae a bad reputation. I'm not sure which is worse - valona or grape caulerpa :P.

If you're intent on keeping the rock 'live', as MarkoD suggested, try a foxface. To add to that you can also try to find and buy a few lettuce nudibrachs. They're a type of sea slug that sucks the 'juice' from caulerpa and uses it for photosynthesize in their mantle. I've never used either fish or nudibrach so I can't say how effective either type is.

The sure fire way is to throw out the live rock that has the grape caulerpa growing on it. If you want to re-use the rock, let it dry out thoroughly in the sun for 3+ months before attempting to introduce it into your tank again.

You can always save your blue shrooms by chipping off as much of them from your rock and transfer them to unaffected rocks in your tank.