Hello @Malakah & welcome to R2R ! I agree, with Retro. I'm certainly not an expert on this. However it does look like a bacteria of some type. we need some more info like age & size of the tank . Parameters etc. I will guess & say the nutrient levels ( No3,Po4 ) are low.
We need to know what kinda light maybe a pic of the filtration. How about flow . Stuff like that.
Par;
T: 27 C/ 80 F
Ammonia :0
Nitrates: 0
Phosphates: 0.15
Calcium: 480
Mag: 1400
Alk: 11
Took all rock out, no smell at all, dosing Nopox 2ml and vodkavodka 15ml
Tank is 150g with 2 clowns, algae blenny, lisptic tang.
Few zoa colonies, frogspawn, elegance, few montis, gsp and mushrooms.
Feeding frozen shrimp every 2 days and some flakes for clowns daily.
Cuc is 5 hermits, 10 nassarius, 5 bumblebee snails few stomatella and sea hare. Tank is full of copepods. 2 bm curve 5 skimmers, carbon and filter socks.
2 rw10 powerheads running 100%
Dsunny reef light on 4 seasons cycle,
10000l return pump running on 100%
No refugium but some macro algae in display.
And tank is 8 months old.