This experiment teaches us a valuable lesson. It also underlines the main message of the video: nature is not fixed, but dynamic. There are so many mysteries contained in it, that we are trying to rationalize, but probably never will. A lot of it has to do with the fact that every environment and every organism is different in some way, even though we try to fit them into categories and say they are the same.
The plants that we as students have are behaving differently. Some plants are dying, some leaves are losing color and there is a difference in root and water color. This makes sense, because even though we all have the same plant, each plant is in an unique environment. We all do different things to our plant, with regards to water changes and light exposure, thus each plant will behave differently.
If we look at it like that, then why are the plants in the lab not all producing the same results? All plants and fish are in exactly the same condition and get exactly the same treatment, but some have higher levels of nitrates then others, to make but one example. Also, three of the fish that are not isolated died. This may be because these fish are aggressive and cannot live with each other, but if so surely all the fish in that condition should have then died? Why those three specifically?
In my opinion, all these questions have the same basic answer: not every organism and not every plant are exactly the same and will thus not behave in the same way. We as humans are each different, so why is it that we assume that organisms belonging to other domains should be the same? Does it all come back to the power-position, that we consider ourselves as special and dominant?
As I said, every organism is different. They each have their own lives, may it be swimming away in their little share of water and reproducing so that other organisms can feed on it and survive, or slaving away in their little cubicle and researching so that other organisms can feed on them and survive.