Hmmm.....looks like you've got a ton of cyanobacteria (the red stuff) there. Do you have test kits? Can you tell us what your readings are for pH, nitrate, nitrite, specific gravity and anything else? If you don't have any test kits, take some water to a trusted LFS
and have them test it, then buy some kits. The Aquarium Pharmaceuticals Saltwater master kit is a good start.
Also, what lighting/how long is it on, and what is your water change schedule? Looks like you've got a decent amount of LR
in there. DO you have any powerheads for water movement?
My first suggestion would be to mix up a batch of water and do a large water change. I'm relatively new to SW
so I'm not totally up on getting rid of cyano
tanks but someone else who is will chime in. My guess is that your nitrates have slowly climbed and finally got to a critical level.
Don't give up, we'll figure this out! Let's hope your sixline makes it, too...moving him to another tank (the LFS
might be a good bet) until you get your tank under control might be a good option too but let's wait and hear from some other folks first.