It has to be adult size I feel no matter what you use. I use it as a guide but I'm adjusting on the fly for differant fish types. So strictly speaking it doesn't work just as is.
Regardless, you are still going to need water changes for a number of reasons. For reference on the amount of plant material this is an old picture of my tank. It is now WAY more overgrown than this. I still have nitrate issues with my tank.
Plants aren't going to pull all of the nitrate out of the water. This is going to be especially true if you aren't actively dosing fertilizers in the water. Assuming that you do a very very minimal amount of stocking, then sure it can help keep nitrates under control however nitrates are far from the only thing that we change our water for. You are still going to need regular tank maintenance.
Also, looking at the video I am 100% convinced that he is not an aquarist seriously looking at setting up a balanced system. His choice of water conditioner alone tips you off on that. The conditioner coupled with a fish load that would require a 60 gallon tank under normal stocking guidelines not counting the fact that those are likely common goldfish which will need a MUCH larger tank. When researching aquarium topics you really need to take the source into consideration and this is a prime example of that. So in short, don't expect miracles.
It came!!!!!My 200 litre tank is coming today!!!
It came!!!!!
Once it's set up I'll send the photos but that will sadly be in a few weeks because without water it's heavier than my 60L full of water!!!Pics or it didn't happen!