Swimming Decorator crab

I have this bubble algae growing in a few places in my tank and in some places it is very heavy. I am not worried about it and kind of like it, but anyway, I noticed that it is just growing on my home made cement rock or the cement on bottles and none of it is growing on any real rock.
It started in my algae trough which is a screen coated in cement. The trough was so filled with this bubble algae that it overflowed and the entire thing fell into the tank from the weight.
I find this ...

I haven't really posted here before, in the blogs anyway but I have some time and some pictures so what the heck.
As some people already know, I set up my reef in 1971 and so far it is still running. Ug filter and all.
So I figured I would post a picture. It is a 100 gallon mixed reef with a few SPS but mostly LPS corals and about 20 fish. All of the rock I either collected myself or built from PVC pipe covered in cement.
I recently changed from MH to LED.

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