I also feel that the person in the video was moving the vac too fast. She was kicking up a lot of detritus. I wouldn't be surprised if she caused an ammonia spike.
It's also, IMO, much easier to do than the video presents. I would definitely recommend a bucket clip to attach the hose to the bucket. You don't want the other end of the hose to start spraying water all over the room if it gets loose. I don't fill my hose up with water to begin. I just clip the hose in the bucket and put the siphon in the tank. Submerge the siphon tube completely under water and then slowly lift it out and up, so that the open end is pointing straight up at the ceiling. The water will start to go down the siphon and into the hose - let the water start to move down the siphon. As the water is going down, submerge the siphon again and the water will continue to flow down the siphon, down the hose, and into the bucket. Now you've got the suction started and you can begin cleaning.
The key is to keep the water moving down the siphon tube, and then submerge it quickly. If you don't lower the siphon underwater fast enough, the flow will stop, but just restart it again. It does take a little bit of practice.