Micromussa skeleton growth?

[Kobooi]

Since a few weeks I have a few micromussa frags on my rocks in my tank. They are growing small new heads, like the green one:

However there is one frag, the red one below, which does something different. Instead of new heads, it seems it's "closing the gap" with the rock by growing white skeleton (?). Is this normal? Will all my frags do this eventually when they run out of real estate on the plug? Or is this something else and has it nothing to do with normal growth? I can't find any similar picture online.

 

[andrewkw]

That white skeleton appears to just be sponge growth. Overall your frags look mounted pretty good, they will eventually go down the plug and onto your rock work. Ramping them is the way to go. Often people just place them on the sand and they grow around the plug with the new growth never getting any light or having anywhere to go.