Little tentacle things growing on glass

[Jake_the_reefer]

So just as the title says I have these little tentacle things growing on the glass of my reef tank, the tank is 4 months old and all parameters that I know of are perfect. I scrape the glass but at least 10 appear a day does anyone have any idea what they are and if they are safe or should i do something about them

 

[James M]

Medusa hydroids maybe

 

[Lovemyreef2015]

+1^^ they normally go away on their own. We had some for a few months when we first set up our tank.