We use sunlight and shade cloth out at the lab where I grow my weeds.
I use soil, typically a 3:1 sand: soil mix.
If I want to amplify growth to get more weeds, I will add KNO3/KH2PO4 etc, but typically it's not needed.
I have hard plumbed water changers on the 300 gallon coffins and set at a slight drip, so it gets plenty of water exchange.
When folks claim no ferts, they mean they still add it to the substrate...........and the tap and the fish waste are also ferts in all cases....
Tap has Ca/Mg/NO3/PO4 in a combo or at leats one or two of these.
Fish waste has them as well.
So you still add ferts..........it's deceptive to say you do not