Help with Zoa

[Ratkiller]

I've been having trouble with my Zoa. Actually I have never had great success with them. Let me explain; after purchase, they always open up and look great, their stems usually always extend an inch to a half inch, but they never spread or I should say grow more heads. And this is in a 55s with 5g fug, 20g sump and has been established for 3 years. All my parameters are in normal ranges and I do 5g water changes every week. I looked at some pics from about 6 months ago and my Zoas looked great dense. But now they are looking very sparse. Please take a look at this picture and tell me what you think. In the red is legs. they look like tiny serpent star legs. Could this be a Zoa Spider every talks about? And in the yellow the mantel or matte in-between is turning dark purple. I don't know if that's normal but I though it is worth mentioning.

Any input would be appreciated.
http://s202.photobucket.com/albums/a...rent=close.jpg