What is on the glass?

[jaha258]

Hello! I’m new to saltwater. My tank is a 10 gallon, and it has been running for about 4 weeks. Ammonia and nitrite are both 0 (they both have risen and lowered) and my nitrates are between 0-5ppm. I’ve been using RO/DI water as well. Yesterday, I noticed what I think are diatoms on the rocks and sand, which I’ve read about and understand they should disappear on their own (please correct me if I’m wrong). Today, I noticed these white things on the sides of the glass. Could someone tell me what they are? And if they are okay to have and how to get rid of them? Thanks!

 

[vetteguy53081]

Hydroids. They can multiply and feed off suspended food matter. Simply scrape off with an old credit card into a net and discard

 

[jaha258]

Thank you! How did they get there in the first place? Once removed, will they come back?