Noticed mine took off after application as well. Roughly twice as big as last week. Excited to see if there is any impact late flower. I suspect that mycorizea and bacteria still attach to roots and provide secondary metabolites as the root mass gets larger.
I feel like many people think these colonies can’t form in hydro because of the constant movement, but root balls can get quite dense. I think some colonies still exist, perhaps not in an ideal environment, but life generally makes a way. If they do attach as I suspect, they still provide immune health to the plant despite their lack of function for delivering nutrients. They still make these root zone secretions, altering ph in the rizosphere. Just my 2 cents. I’m no botanist though.