Id please

[Thanhk87]

Just want to know what this is. Is it harmless or something i should watch out for. Its spreading like wild fire.https://uploads.tapatalk-cdn.com/20190203/8b2917b562db8b0fad0db4636ee5d0fc.jpg

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[Goomba]

It's a harmless type of hydroid. They usually have a little population explosion then taper back to near zero.