Resolved What is this on the tank glass??

i have loads of these on the glass of my tank.
what are they??
are they good or bad?

 

photos?

 

photo added

 

hydroids

 

Those look like a type of hydroid. The population in my tank raised then began to fall off almost as fast.

 

are they dangerous to fish???

 

Not in my experience.

 

Hydrozoa

I looked for over a week daily on the web and couldn't get an answer except from here at 3reef forum. What you have are identical to what I have in my tank. I was told they are Hydrozoa which are related to jellyfish from what I understand. I was told to just scrape them off since they won't last long as free swimmers. I was also told to be careful though because they have stinging cells that may harm your fish so wear gloves if you stick your hand in the tank. Personally, I haven't had any trouble with them. See my post "Peculiar Protozoa" and threads that follow.

 

their population will explode and then crash. thats what happened to me when i started my tank.