Zoas and Shrooms can will and do cohabitate well together in captivity. I agree with BrokkenTWolf and mfinn that concern and not caution is the optimal word when it comes to keeping both. If you view the picture in the link below of my tank, you'll see that every single colony in my tank was grown from less than a 1/3 of there current size with the exception of 3 ricordea colonies which had grown to about double their original size if I recall correctly.
When my zoas began expand towards my mushrooms I had the option of either removing the zoa rock, which isn't always possible, then removing 3 or 4 rows of zoas with a chisel. It would scar the rock, but in a matter of days to a few weeks the rock would become encrusted again. I could either sale the frags or attach them somewhere else on the reef.
It's true that mushrooms will expand outward and prevent the zoas in close proximity from receiving light which will eventually prevent the polyps from flourishing. Again, fragging or moving one of the two rocks will solve the problem.
When I saw that my growth was maxing out throughout the entire tank, I had to cut my photoperiod by 3 hours sometimes. It also gave me a reason to leave my tank completely dark once every 4 days or so. I never had, saw or witnessed any ill affects from doing this and I do it to this very day as well. A dark tank once a week is no different than a cloudy, dark overcast or stormy day in the wild.
As BrokkenTWolf said, you can space them out, which works fine until your growth causes them to compete for space and light.
lildraken, Ricordea are typically slow growing Corallimorphs. Expansion would be my immediate concern. If the zoas are on the far ends of the rock I would leave them alone. Wait and see how fast or slow they reproduce. If in time you can see that they are indeed growing and spreading towards your shrooms, I would begin fragging them periodically and seeding new/bigger rocks to sale or place elsewhere in you tank. You could also use a hammer and chisel and severe the entire portion of the rock with the polyps on them. Another option would be to secure several small chips of rock around the perimeter of the zoas. Using some reef safe glue, use a single dab of glue and secure small 3/4 inch chips or rock around the zoas, kind of like placing rocks around a camp fire. As the zoas expand outward and over the chips of rock, and since you only used a small dab of glue, just break off the chip of rock with the new zoas and Wah-lah, you have a new frag to sell, trade or keep. Or, you can just place the chips of rock between the zoas and the shrooms and keep the expansion towards your shrooms at bay.
Didn't mean to be long winded. Good luck my friend.
Mucho Reef
