your post made me smile.
Nobody is going to kick you out of the forum for experimenting with dosing. Your tank is an El natural setup but it seems that the soil you are using might not contain the same level of nutrients as other people's soil so it helps when you add nutrients.
Salvinia is a nutrient demanding plant so it makes sense that the water column is devoid of nutrients like phosphates.
The hobby of keeping aquarium plants is not one with a pre-written formula for success. Everyone has a slightly different spin on the general themes. For you, adding certain extra nutrients helps your plants grow. What you are doing is perfectly fine. After all isn't this hobby all about getting the plants to grow best?