Urgent Please help identify aggressive unknown colony in substrate

Really hoping you guys can help this is quickly turning into one of my go to forums. I've been keeping cichlids for years, and always wanted a reef tank. Finally, I have an incredible display purchased used. 27g hex tank running around 8 years. I will be searching for a mentor to help me keep this tank beatiful... any volunteers!? First and most importantly though, I have a huge colony of something filling my substrate behind the rockwork. Due to the size of files, I have created a channel on youtube documenting the tank and everything in it. Also, are several other videos of the surprise guests. The videos show the creatures in vivid detail, and the rest of the tank in decent detail so I'll skip all that stuff. A few notes about behavior, in case it helps. They mostly disappear when the lights come on aside from a few well shadowed areas and a couple that are busy eating. They may move to get to food sources, but mostly just stretch to reach things(also documented in videos). They don't appear to be harming fish or shrimp, but do appear to be actively and successfully killing snails of varying types. Crabs on the other hand appear not to mind them, actually saw a brave scarlet reef crab digging in the substrate in the middle of the colony(when lights were on and most of the unknown colony was hiding. I attempted to scoop one up and it immediately retracted lightning fast. I tried digging deeper and a hole appeared where he was so apparently they go pretty deep. Also, there are a few on rocks in shadowed areas and in old shells against the glass in the front of the tank. My concerns are mostly obvious, but I'll mention them anyways. Are these things going to spread, start killing more valuable things, do I need to wage war against them, if so then how would I do that, what are they so google can help with my education. Like I mentioned I am new to all of this and want to avoid as many hard lessons as possible. Also, on a final note, any other feedback will be much appreciated. Aside from the clownfish, pin cushion urchin, kenyi coral, toadstool leather, green mushrooms everywhere, and the unknown red polyp colony with feather duster I found while bringing tank home, everything else is new. I am researching placement and compatibility as fast as I can, but i'd guess the pros could see what's right and wrong with a quick glance at the video. I'm guessing the first comment will be that the frogspawn is in a horrible location next to and under the toadstool. Just got it yesterday (the frogspawn, got the tank last Saturday) and a quick google search may have averted disaster. The frogspawn is now where the open brain was and vice versa. Is it still too close? I read that the sweepers reach up to ten inches and they are only six inches apart. My initial theory was that the sweepers mostly go upward, but today, now that its fully open, the polyps aiming toward the toadstool make me wonder if I have some more rearranging to do. On that same note, some of my smaller polyps and toadstool are pretty close to my open brain, which I've read is very sensitive to stings from other corals. I am a very quick learner, but haven't read anywhere how fast a coral will kill another, so I don't know if simple observation is enough. I'll stop here for now, I clearly have a lot to learn and don't want to ask too much all at once. The tank may look like I just put a fortune into it, but its pretty much milked me dry. So hopefully, throwing money at it isn't the solution. Thanks for all you've already taught me, and for all future advice.

Ps will update profile asap with pics and description, but for now it is all listed on channel dbarter8872 on youtube!

 

Welcome to 3reef.

LPS corals can be very aggressive if you are seeing long sweeper tentacles I would move one coral or the other.

As far as the creature or creatures you describe please use photobucket or another media to copy and paste an image into your thread. By doing so you will generate more responses or link your youtube to your thread.

Please review the links below to assist you with common ID's:

Live Rock Hitch Hikers
Melev's Reef - Visual Identification
LionfishLair.com - Hitchhiker Guide to your Aquarium

 

best video of unkown species hiding behind rockwork in reef tank - YouTube
There ya go
That is very interesting. I know there is an LPS coral that is nocturnal and looks similar to that. I'm not sure of the name.

 

Or, they're hydroids

 

Thanks Chance.

Ok you got me, that ID will take a while. If they did not only come out at night I would have thought maybe hydroids, but because they are nocturnal I believe it's some type of filter feeding worm.

If possible remove one, rinse it off and place it behind or one a dark surface to provide contrast and get a macro image if possible.

Edit: you might be right Chance.

 

video of unkown species terrorizing snail - YouTube
This one shows they a bit more up close.
magnified view of a small portion of unkown species colony - YouTube

 

They do look like hydroids, but I am not convinced yet. Maybe Renee will know.

 

RENEEEEEEEE WE NEED YOU!!!!! xD

 

Thanks for the replies. I'm thinking some sort of cnidarian or hydro, but not at all similar to anything I find when searching. When trying to scoop one out it retracted into the substrate like lightning. I tried digging deeper and saw a hole appear as it shot down even deeper. They definitely prefer the dark areas, and nearly disappear when the light comes on. I have shown the video to the owner of a local very trusted shop, and he said he's never seen anything like it. tentacles flow like jellyfish. clear with a purple tint, white specs and rounded white tips. The base is also transparent, but more of a tan to brown color with a very distinct pattern. vertical dark lines at the base with a clear diamond pattern up highter. The center is definitely like a mout and had a 1/4 plus inch snail a half inch into it's mouth. As mentioned once it comes in contact with a snail, the snail never moves again. when feeding on a snail, they don't mind light as much. peppermint shrimp hang out near them, but never in reach and don't appear to mess with each other. coral reef crab sifts in substrate right in the middle of colony with lights on, and doesn't appear bothered yet. I do also see a few on shadowed places on rocks, and there was one in an empty shell in the front of the tank, so I fear them spreading. they will stretch for a snail, and keep going after the same snail after they kill or paralyze it. they also have a tiny orange dot on one side of the top of the base. mostly in small groups, but also in singles, probably over one hundred of these things without needing to count. Just trying to add more info, because i'm really hoping to find an exact name for these things so i can do proper research. They are small, maybe an inch at tallest and just over 1/4 wide. tentacles might be twice the body size and vary in length. they are very beautiful, and if killing snails is my only concern, they might be just biodiversity and a cool thing to observe. More likely, they are bad news and i need to learn about them to decide how to best deal with the problem. thanks again for the input so far and hopefully we'll get this figured out!

 

and thanks chance for posting the links, me and computers don't get along. spend all my time searching for specific things, and only end up finding a bunch of other stuff that catches my attention.