Help!!! Very tiny white critters in the tank.

Hi,

I noticed when I went to go feed my fish that there is hundreds of tiny white critters in the tank. Some are swimming while others are moving along the sides and front of the tank. Under a magnifying glass I notice that they look somewhat like very tiny brine shrimp. Does anyone here know what these critters actually are? Should I be worried?

I've been doing marine aquariums for 10 years and I have never encountered anything like this.

Thanks