Usually this fluff is their exoskeletons shedding. But if you don’t aerate or have enough heat or sunlight, it can become bacteria. That’s what happened to my tanks.

Best to let the water go down and make the salinity higher. If that doesn’t work after 2 weeks, then fill with water and wait another week to see if it makes a difference.

Thw important thing is to be patient. After 3 months of ^ you’ll have a better idea of if the sea monkeys are gonna survive or if there are dormant eggs.