That is the one that caught my eye at first. I would definitely re-home him.
How are the tetras?
How many do you have?
Are they active?
When I did Discus years ago, they were supposed to be kept with peaceful non-active fish. Also, we kept that at higher temperatures than was appropriate for most community fish. I only kept Cardinal Tetras and Otto Cats with mine.
Personally, I think they looked a little stressed in the video. I attributed that to being new to the tank and being youngsters. What made me think they were stressed was the stripes, which are more prevalent when young, and the fins not being fully extended. I think someone said earlier that Discus are not as difficult to keep as they were years ago but any advise from someone who hasn't kept them before should be taken with a LARGE grain of salt. They may be eating and swimming fine but even low levels of stress over an extended period is more detrimental than high levels at a short duration. If you become familiar with the subtle signs of stress, you will be able to react before it is too late.
As to stocking, they get to be about the size of a small dinner plate. The higher temperature of the water also lowers the potential fish capacity of your tank. Warmer water isn't as capable of holding onto dissolved oxygen. I think your current numbers are right for your tank but that is just my personal opinion based on knowledge that is years old in my head.
HTH