This is really good!

Changes:

plants -> clams (the video was about giant clams)

"Up to now is quite interesting, but what it grabbed my attention was to know that" -> "This was quite interesting, but what grabbed my attention was that"

What people usually call giant monsters of the deep in films are in fact, giant plants. These  plants are the largest of their kind with shells over four feet long, but they   and are hardly dangerous as  since there has never been a reported death caused by these plants. In fact, the way most people are hurt by giant plants is by  trying to pick them up as since they can weigh up to five hundred pounds. Life as a giant plant is rather peaceful. They live in coral reefs in the warm shallow water in  of the Pacific Ocean. Up to now is  This film was quite interesting, but what it  really grabbed my attention was to know the fact that each plant has a settled unic unique colour pattern on their skin.

Good  Job!, (not sure what you meant by "settled"...I didn't watch the video) ....Giants monsters of the deep would only be capitalized if it was the name of a movie or a ride at Disney Land or some other proper noun like Pacific Ocean.  

What people usually call Giant Monsters of the Deep in films are, in fact, giant clams. They are the largest of their kind with shells over four feet long, but they are hardly dangerous as there has never been a reported death by clams. In fact, the way most people are hurt by giant clams is by trying to pick them up as they can weigh up to five hundred pounds. Life as a giant clam is rather peaceful. They live in coral reefs in the warm shallow water in the Pacific ocean. Up to now it is quite interesting, but what it  grabbed my attention was to know that each clam has a settled unique colour pattern on its skin.

Well done!