Yep, have a lot of info on these as I fought them a few months ago. I just posted in another thread about this, but will reiterate here as well.
There are several different types of sea spiders. Some of them grow to massive sizes. There are unfortunately a set of them that are predatory to zoos. They hide near the base of the polyp, stick their proboscis into the zoo and literally suck the juice out of them (for want of a better description).
From my research (which was extensive secondary to the fact that I had these suckers), it seems these guys are hitchhikers. They are hard to get rid of. There is info on them here in older threads that you can access. Also, wetwebmedia.com has alot of info on them also. Just go to the site, go to the search and type in zoanthid spiders. I posted there once and Bob Fenner answered me himself.
I have been spider free for about 6 months now. It was hard work getting rid of these little suckers. From advice from others (and research on here and wetwebmedia.com), I removed all of the zoos from my DT that I could, performed a FW dip on them (which will either kill or stun the suckers so that you can see them and pick them off), and then QT'ed them. About every week or so, I performed another FW dip. I continued this until I saw no spiders for TWO MONTHS. Then, I put the zoos back in the DT and have been fine since.
I was new to the hobby when all this started and didn't know I was supposed to QT everything before putting it into my DT.
Others may have different things to add, but this worked for me. These spiders really don't like FW. The zoos are unhappy for a bit, but did fine--except for the ones that were damaged by the spiders. Those didn't make it. I lost a whole frag of radioactive zoos in my DT before I figured out that I had spiders. I found them by accident after lights out one night. I had the old flashlight out looking at the tank after the lights went out and saw them. That's when all the hard work started. Hope this helps!
