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!