Any ideas on why 1 colony of zoa declines while all others are great?

[hillegom]

yes I agree, you have to pluck that macro algae out of there. It will take over if you leave it.
What are your water parameters? Ca Alk and Mag?

[daniella3d]

I go for the hair algae. Zoanthids do not tolerate being invaded by any kind of algae. Remove the hair algae right away as they are making roots in the mat of the zoanthids and killing them.

[hillegom]

Right what I said, get rid of the macro algae

http://saltaquarium.about.com/od/alg...hotos-Gallery/

[toytech]

If the rock is small you can dip it in 6 parts tank water to 1 part hydrogen peroxide .Let it sit for about 2 min and then rinse . Its how i get the HA off my zoas , they realy dont like it and wont open if there bugged . ( ive done this several times and my zoas have been just fine but if yours catch fire or explode plase dont blame me)

[The Grizz]

What about little white feather dusters? I have a ton of them invading a couple of my zoas and the zoas are slowly losing. Don't want to add any kind of fish that will eat them as they would more then likely go after my big colorful dusters. Anyone have this issues?

[MKLKT]

Looks like a little aiptasia on the bottom right of the pics, too. FYI

[mattdean]

check for zoa eating nudibranches.