May I know What micro organisms in my saltwater aquarium seen under microscope (parasites or rotifier ? )

[satheeshg15]

I was having a clownfish in my 2 feet tank, All of a sudden it jumped out and died. Later I bought and around 5 clown fishes, it all died within a week.
Later I found some little things were swimming in the tank and it multiplied so much. Then i took a drop of water and looked at it under microscope. I am not sure it is a parasite or rotifiers. Could someone tell me what is that ? I am attaching the video

 

[AlyciaMarie]

Hey friend! I'm having trouble viewing your video. Can you upload via YouTube?

 

[Court_Appointed_Hypeman]

What magnification is that?

 

[ISpeakForTheSeas]

I was having a clownfish in my 2 feet tank, All of a sudden it jumped out and died. Later I bought and around 5 clown fishes, it all died within a week.
Later I found some little things were swimming in the tank and it multiplied so much. Then i took a drop of water and looked at it under microscope. I am not sure it is a parasite or rotifiers. Could someone tell me what is that ? I am attaching the video

Looks like they may be Dinophilid worms, probably Dimorphilus sp. worms more specifically - they're not harmful; they're good.