Cyano - It's just a spot, but for how long?

[Calm Blue Ocean]

So yesterday I came to the realization that the colorful spot on one of my rocks was not a sponge and not coralline but rather a rather spectacular looking dab of cyano. Right now it seems pretty localized but I've had cyano take over a tank before so I'm not feeling happy about it. The rock it's on is structural so removal isn't really an option, but the offending spot is fairly accessible although it seems to go down into the rock a bit.

If I try to scrub it will I spread it? Maybe I should just drop a big shell over it and block the light? What about dripping some peroxide on it? I have hermits, astraeas, ceriths and trochus snails, will any of them eat it? This stuff is bright red and even fluoresces under blues.

I'm just starting to be happy with my tank, why does this kind of thing always pop up right after I start thinking things are looking good? Last time it was dinos. Not sure if this is better or worse lol.

 

[Spare time]

It probably isn't an issue. You can just brush the spot if you want. Just make sure to keep nitrate above 0ish and phosphates below .1 ish

 

[ColoredRock]

Siphon and a toothbrush