unhappy zoos

[newfound77951]

I have several colonies of zoos of various sizes, from a few polyps to a huge completely encrusted rock. Two of the colonies seem to not be very happy lately, the polyps remain closed except for one or two. One piece of rock has a small Valonia on it but it is not touching the zoos. the pieces are on the bottom of the tank, haven't moved. Other zoos are higher up in the tank and are fine with the lights. Any ideas? They don't look eaten, and it's just these two colonies, but i know I have a few potential nibblers in the tank.

Tank specs:
30g long
4x39 watt T5s
BakPak skimmer
pH 8.0
temp 78
nitrate, nitrite, ammonia 0
phosphate 0
various zoos, mushrooms, soft and LPS corals
3 fish (pygmy angel, hawkfish, 6 line)
cleaner shrimp and emerald crab
2 feather dusters
zebra hermits (one large one)
astraea and nassarius snails

 

[melosu58]

Looking at your tank inhabitants I would agree you might have a few suspious characters there. Try to keep an eye on them and maybe even for some hitchikers that might be out at night.