I've got a bit of an emergency here! Background: I bought these two acropora frags (one yellow and one reddish) attached to the same rock about three months ago. All was well until a few weeks ago I noticed the yellow frag had some tips turning white. I thought this might just be new growth, so I left it alone and decided to just watch the situation. Then, I looked yesterday, and the yellow frag had lost ALL of its color OVERNIGHT--it's now TOTALLY bleached, and had a slimy coating coming off of it, which I assume was the old Symbiodinium that had left the coral. AGH. Thinking this might be bleaching from too much light, I moved the coral from the middle of my tank to the bottom. But now, one day later, the reddish frag has had the same thing happen! I've attached some pictures--the previously-reddish frag is the one with slime coming off. I'm at a total loss about what to do. I did notice some green tube-like things (third picture) coming out of the rock when I first got the frags, and there *might* be more of them now--I thought they were just plastic at first, because the "rock" had some other weird plastic pieces sticking out, but I guess they could be some kind of parasite? Other than than, I have no ideas what to do. If this were light-related bleaching, it wouldn't have happened so fast, would it? ANY advice is hugely appreciated!
28-gallon JBJ Nano Cube
150 watts of LEDs—10,000 K
white and royal blue
Two 425 GPH
powerheads (malfunctioning as of a few weeks ago, getting more like 200 GPH
Two 300 GPH
5-gallon water change every 2 weeks
Feed mysis shrimp, hard pellets, Phyto-Feast
Calcium: 360 (I know this is low; I haven't checked it in a few weeks--but this alone couldn't cause such dramatic bleaching, could it?
Temperature: 79 degrees F
1 melanurus wrasse
1 red fire shrimp
1 red starfish
Turban, turbo, nassarius, and nerite snails
Acropora, montipora, birdsnest, zoanthids, blastomussa, ricordea, lithophyllum, leptoseris, pulsing Xenia, galaxea