Changing blocks in a circular pattern from single location

Hello all!

I don't really know how to explain this one, so I have this piece of code to help me explain it:
http://hastebin.com/majupamaqo.avrasm

Anyways, from a certain block, I want a sort of infection to start. From the starting block, the infection will spread to each neighboring blocks and then continue spreading from there on. Like if you were spill water, the water would expand outwards from the spill location. If that makes any sense.

The only issue is, that with my code it gets pretty laggy after a few seconds. In a perfect reality, I would like the spread to occur every second and spread randomly. There has got to be a way to do this without any lag, but how?

Thanks,
HeyAwesomePeople

 

@HeyAwesomePeople

Can you give a bit more information? How quickly should it spread? How consistently?

 

I was thinking each second or little fast it would spread outwards one block in all directs. It would change the blocks it's spreading to into a colored clay block. This would continue until it spreads to the whole area(set with a cuboid) or the head mob is defeated.