What is this grown almost overnight?

[nthanhalan]

I just this grown on my rock today. The rock is almost cover in yellowish layer of something, maybe algae. There some hair growing too.

Can someone tell me what is it and is it safe for the tank? Could it spread from this coral?

 

[Skep18]

Are you speaking of the brown, tentically, aiptasia looking stuff?

 

[nthanhalan]

Are you speaking of the brown, tentically, aiptasia looking stuff?

Yes and now it growing on the rock. I swear just yesterday the rock were white

 

[Coralreefer1]

You have some algae growing which is normal, and with minimal nutrient levels should subside. Also, janitorial crew like snails and hermits can help to maintain it. Aiptasia anemones are a big problem, however! They need to be removed sooner than later or you will have a large population of these as they are prolific reproduces. They can wreck havoc in the presence of corals. Stinging nematocysts will injure your corals or cause them to not open up.
The whole anemone needs to be removed or small pieces of itself will reproduce. A kalkwasser paste, vinegar, lemon juice, Joe’s Juice or comparable liquid or scraper/ tool for eradication will work nicely.