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These are Hydroids. Manual removal is the best way to handle getting rid of them. Pull the rock out of water and use tweezers to get them off. Other methods although not totally successful includes kalkwasser mixed into a thin paste, and Joe's Juice. These droids WILL sting corals that they come into contact with. Cutting down feedings will often help but often will not take care of the problem completely.
They were probably pre-existing and will eat any food they can grab, especially brine shrimpI don’t feed a lot. I just put fish in the tank a week ago and they just started eating a couple of days ago. Whatever food they don’t eat I scoop out with a net. I will continue to manually remove it like I’ve been doing. Thank you so much for your help.
If I'm not wrong They feed and from the lights, or at least suspended particulate matter & plankton, will be hard only with target feeding to control them population.Try to target feed only. No broadcast feeding. Hopefully you can keep them in check. Good luck
Thank you for your help. I definitely will be getting a magnifying glass so I can get all off them off.Hydroids, only I don't think they can sting anything (had to fight with different sp. hydroids during the last 2 years), but they can really fast overpopulate the entire of your tank, and to start shade and disturb some corals.
Joe's Juice never help me, kalkwasser block them for a while, and they will find how to appear back again. At the moment I'm fighting with brown colonial Hydroids (on a LR with zoas, before I put it in my system), only under magnifier taking off the last bit of them (the small tube connections between this have to be removed 100%). None "reef safe"can treat them (or I don't found anything which can). Be careful, they eat suspended food from the water, and also this are and photosynthetic, but cutting off the lights isn't killing them. And they can return back just from single cell (that's one of the reason they to destroy many reef tanks thru the years).
but you have to have on mind that, if by some reason something go out of the range in to your tank, and if that out they love it..., just for really short time you will be overpopulated, w/o chance to go rid of them, they aren't like the diatoms, and aren't aging. I test them (the white SP and brown colonial) calcwasser, aptasiaX, - seal them for a while ; lemon juice, vinegar, fresh water(3-4 minutes) - that method give me similar results, but it double them spreading after they come back (and they become partially immune the fr. water), I try and Dettol -Antiseptic, it kill them only if keep in the solution over 10 minutes double the concentration (Dettol Antiseptic 4.8% Chloroxylenol, I'm using deluted in tank water 0.5ml-0.7ml per tank water in separate container for 5-7 minutes dipping new corrals) even the peroxide 3.5% for about 2 minutes don't give any results (can't dip anything longer than 2 minutes in 3.5% otherwise make good damages to the coral in)I used to broadcast feed my tank with reef roids. After noticing these colonial hydroids I decided to cut back on the feedings and broadcast feeding. The hydroids are also photosynthetic but reefers said even light starving them will not work effectively. I have not noticed the hydroid population decreasing but it has not increased over the past few months. Its the more natural way of doing it IMO, I do not want to remove the rock either.

