Who eats ricordea and zoo's

[cag]

I have had my reef tank growing and developing for three years. It has gone through several upgrades to bigger systems, and I made a move last fall to a 90 gallon system. At that time I added a bunch more rock, but was carefull to put in only rock that had aged at least 4 months, so the system didn't seem to cycle that much. But ever since thankgiving my beautifull collection of zoos and ricordea have been shrinking back and then dissappearing. I have watched day and night for offenders, but have only seen one long worm, slim and smooth that retreats from light grazing once near the base of a coral. Here is a list of what I know is in there, does anyone know if I have been missinformed on something from this list. As far as I know nothing here is a problem.

Fish
Yellow Tang,Purple Tang, Sailfin Tang, Regal Tang,Timini Tang, Clown Tang, and Powder Brown Tang. 2 Chromis, 2 red blue strip damsels (new), a cleaner wr**** a six line wrass (new),2 maroon clowns, 1 ocelaris clown, 2 yellow watchman, 2 orchid fridmani, and one small batfish.

Inverts
4 cleaner shrimp, 3 pepermint shrimp, 1 fire shrimp, 2 dappel shrimp, 1 mini coral banded (purple body, yellow, white , red striped legs), and one tiger prawn (ornate looking patterns almonst like a mandarin dragonette, but in tans and golds. He is shy, only comes out at night, and has filter feeding front legs). There is also a Sea Hare, a cucumber, astria snails, pyramid snails, about a dozen zebra hermit crabs, 5 boxer crabs, 3 red footed snails (they do have a spike on the front of thier shell, but I have never seen them attack a coral.) a red formosia starfish, a blue leathery speckeled starfish (that I have had from the begginging so I know it is safe), some feather worms, and serveral bubble tip anenomies.

Coral
finger leather, 4 kinds of star polys, 3 ricordea left from the original 12, 10 zoos left from the original 16. one favia, 3 other mushrooms, 3 different trumpet corals, a torch, elepant ear, and 2 sps corals.

My water has been fairly stable. Skimmer works fine. Ph 8.2, calcium between 380-420, temp 81, KH good, nitrate up a bit at 12-15 (but manged), no nitrite or amonia.

The corals look awesome, then one day the zoos will not open, and then over a few days to a week the colony dissappears. The ricordea do the same, they shrink, loose color, look damaged or mushy, and then they are gone. It seems to effect only a couple at a time, others look fine, till it is their turn. I bought the six line hoping he would eat any small offenders. Any ideas would be greatly appreciated.